'03 Suburban Quirks

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Hey guys,

Quirk #1 that I'd like your opinions on is a strange intermittent noise. It only happens on a cold start, after sitting for a couple days. It sounds like a low, sheet metal-esk shudder, like part of the exhaust system or heat shielding. The thing is, it ONLY happens after a couple days of sitting and ONLY for a fraction of a second between engine cranking and idle. The noise is gone before you can let go of the key. Sitting in the driver's seat it seems like it's in the engine bay, not under the truck.

At first, I was thinking possible lifters leaking down, but there is no lifter tick, ever, and if it was leaky lifters, wouldn't it present itself more often and for a longer duration. it's also more of a sheet metal rattle than metal on metal pinging/knocking that lifter tick usually presents as. Now I'm leaning towards heat shielding, but again, why would it be sporadic and only on first start of the day after sitting for several days and not all the time?

She's been sitting now for a few days and I'll be driving her tomorrow. I'll try to come up with a better noise analogy, possibly have someone else turn the key while I poke my nose under the hood, until then, all opinions welcomed.
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I wish mine would only do it for a quick second. I've replaced every tensioner, pulley, and belt. Mine doesn't make the noise without the belt. 02 GMC with a 496/8.1 big block.
 
I also have a startup noise like you describe, sounds like after 1 cycle of the pistons it is gone, which I thought was just oil leaking down. It makes me cringe every time. It does it each day, worse when left to sit for a couple days. I park my truck front up up on a slight incline if that matters. Another thing I notice that it is worse as the summer is getting hotter here in Florida. I notice you are in CA, so maybe it is temperature related? I also have a bad knock sensor that eventually needs replacement, don't know if it is related or not.

I also just had my driver side Cat converter cut out of my '03 Suburban. Sounded like a rapping rod.
Not saying that is what your problem could be, but mine started very gradually, initially only slight sound coming from what seemed drivers side engine compartment at cold startup and went away when it heated up. It got worse each day and eventually I had it removed. Inside the honeycomb material came loose and was broken. Maybe you are hearing a piece of that material against the cat converter housing?
You could tap the converter with a hammer to see if you can duplicate that noise.
 
For what it's worth, the Burb is new to me, I bought it the end of February and it did it back then when the temps were in the 50'-60's

Hmmm, hadn't thought of belt slap, but that is exactly the kind of vibratory noise I'm hearing. I might just have to pull all the belts and see if it does it.

The Burb is parked on a flat driveway, oil is fresh-ish (changed in Feb.) and at the proper level. It's checked often because the oil filter leaks slightly, but not enough to warrant changing it before the next OCI.

The rattle does sound a bit like an exhaust rattle, but I would think that if it were a cat, it would do it virtually every time it's started up and not just occasionally after sitting for several days. It's no worse today than 5 months ago when I bought it.
 
Knock around on the catalytic converters.....The catalyst heat shields are bolted to the body. People have a tendency to bend-up the passenger side one getting to #8 spark plug on vehicles with auxiliary HVAC.

The exhaust manifolds have heat shields bolted to them.....Make sure all the bolts are present & the shields are tight.

There is also a heat shield bolted to the passenger side of the trans, Make sure it's tight
 
Great tips, Cline, thanks. Yes, the Burb does have the aux. AC unit in the back of the truck, so it's likely that someone's been in there bending/moving heat shields.
 
I have heard some odd noises on cold start that seem to be specific to hydroboost equipped vehicles. Assumed maybe it was the accumulator pressurizing, never really gave it much thought otherwise. No idea if any of the above mentioned have hydroboost or not - tho I'd assume the 8.1/496 does.
 
Ok, I think we scared it!
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She's been sitting for about 4 days, hopped in this morning and it didn't give the customary flutter/rattle/vibration she normally does after sitting.
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not that I'm complaining, mind you.
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I have an 02 Yukon 5.3 that does that. When my vehicle sits several days it revs instantaneously up upon start up, higher than a daily start up and just for a second then idles down a bit, it does not do this if I drive it every day. I cannot prove it, but I think it is the cold belt slipping on one of the pulleys upon the instant rev up, as the engine revs quicker than all the cold belt/accessories can come up to speed. Although it sounds different, maybe because it is cold, but it would be similar to some diesels that chirp when shut off. That chirp is the belt slipping because all the accessories and belt cannot stop as fast as the engine does, and you get a belt slip chirp. In any event, I don't worry about it.
 
Thanks for the input Todd.
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I fired up the Burb yesterday, after several days of sitting. This time I was standing outside the door, reached in and turned the key. I hear the flutter/rattle both under the hood and under the drivers door, which is pointing in the direction of heat shielding or the cat, as someone mentioned earlier.

I really want to figure out what's going on, simply because weird noises and rattles tend to drive me nuts.
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Be that as it may, I don't have the luxury of time or space to dig in at this very moment, however, I am taking note of everyone's suggestions and will be going down the list as soon as I have the opportunity, probably a couple weeks.

Again, thank you to everyone who has participated and offered suggestions, I will continue to update this thread as I have more to share.
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I think if it was the belt in your case, you could hear it as you describe. Belt noise would echo off the ground and you would hear it under the vehicle, as well as under the hood as you describe.

c502cid reported above that his does not make the noise when his belt if off the engine. So in his case, no belt spinning = no noise.

Keep us posted, there seems to be a number of people searching for the cause.
 
Quick Update:

6 months of ownership now with no major complaints or problems to report. I think the trans is shifting better now, I can actually feel most of the up-shifts, whereas before the only way you knew there was a shift was by the rpm change, unless you were really getting after it, then the shifts were a little more pronounced. I'm guessing that a Suburban is considered more of a "car" than a "truck", so the shifts are designed to be more gentle, car-like, than kick you in the butt truck-like. Still, I think they could be a little more firm and I suspect that exchanging more of the tranny fluid than what a typical pan drop/filter change does, would accomplish this goal. For the record, when I was doing the pre-purchase inspection, the tranny fluid was not discolored and there was no strange odors. Upon purchase a fluid/filter service was done.

I don't have the luxury of time or space currently to start going back over everything that the inept shop did or didn't do. I've kept a log of everyone's suggestions and will be tackling the list, hopefully within the next few months.

Another quick update:
Quirk #1 - the strange rattle/flutter noise that started this thread. It sounds like a loose heat shield or something along those lines, the odd thing is that it only happens after several days of sitting, one would think that if it were a loose item that it would happen at every start up, not intermittently. At any rate, I noticed that the plastic engine cover was really loose and couldn't be tightened. I gave it a good shake and it kinda sounded like the rattle/flutter that I've been chasing down, so I took it off. It's been 3 weeks now and I have not had the noise return. Hard to believe this is the problem, but certainly an easy enough fix if it is.
 
Reinstalled the engine cover today. It sits very loosely in the mounts, so I put some thick vinyl tape around the slip ears and a washer under the hold-down bolt, it now sits much more securely. Fingers crossed the rattle/flutter is a thing of the past.
 
Originally Posted by another Todd
If that's the case why would it only happen after it sits for a couple days? I just accept my noise now, nothing to worry about.


That has been my question all along as well. Does the engine shake harder upon startup after a sitting a few days, more than it shakes during any other start? Seems a bit odd to me, but
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It's pretty common for that era GM V8 . Some call it a piston slap. Only happens at startup when the engine is cold and the oil just starts flowing. I found the combination of thicker oils and high efficiency oil filters makes the sound a lot worse. I have all but eliminated it on my 6.0 with the use of a quality 0w/5w synthetic oil and lower efficiency oil filters. I can't use the Fram Ultra, Mobil 1, anything like that. Fram tough guard, ACDelco, something with higher flow. I think it's the oil pumps used. They just not that strong.
 
Also take a peek around the engine and make sure you have all your exhaust manifold bolts. If you're missing a few which most are that can sound pretty bad until there is some expansion to tighten up the exhaust manifold leak
 
In the shop I have a service bulletin from gm that says the cause is non floating wrist pins. The bulletin I have is on the 5.3
 
Thanks for the input guys.
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I'm pretty certain that it is an external engine noise. As earlier mentioned, I pulled the plastic cover off the engine and the noise virtually vanished. With the engine cover now back in place, it's a regular occurrence.

It's definitely not lifter tick and it's definitely not piston slap, the '02 Sierra I drove up until the first of this year had both of those things. This noise with the '03 Suburban is definitely something else. The "flutter" is only for a split second between the moment the engine catches and the moment it is idling. Lifter tick and piston slap both take much longer to dissipate.
 
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