1,900 RPM rattle diagnosis help

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The GP (supercharged GM 3800) has developed a strange rattle/scraping sound. It comes from the passenger side of the engine compartment and sounds sort of like a loose heat shield vibrating against a piece of metal or metal blades scraping against metal. It only happens at 1,900 rpm under light/medium load, such as when slowly accelerating or going up a slight incline, and seems to happen more often when the engine is fully warm than when cold. The noise stops if you raise the rpm to 2,000 or drop to 1,800 and does not happen if you just run up through the rpm quickly. It can't be reproduced for any length of time when parked because it needs that load; I can be parked and hold the engine at 1,900 rpm with no unusual noise. And it is not speed/gear dependent: it happens at 35 mph on city streets or 65 mph on the highway. Also not dependent on A/C or heater operation as it happens with it both on and off.

I have checked for loose heat shields and cannot find any.

Any idea what it could be? I'm at a loss and will take it into a shop for diagnosis later this week if nobody here can help me nail it down.
 
Its the supercharger coupler you have to pull the blower nose to replace it. its a 20.00 part and you have to replace the oil in the supercharger at the same time.Search for the noise on utube and look on ebay for the parts to fix or zzp.
 
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Originally Posted By: cknight49090
Its the supercharger coupler you have to pull the blower nose to replace it. its a 20.00 part and you have to replace the oil in the supercharger at the same time.Search for the noise on utube and look on ebay for the parts to fix or zzp.

This!
Easy Fix. It is plastic. I guess it is in case something locks up, that way you don't break everything. The get loose as they age.
stock coupler
aftermarket coupler
 
Originally Posted By: ls1mike
Originally Posted By: cknight49090
Its the supercharger coupler you have to pull the blower nose to replace it. its a 20.00 part and you have to replace the oil in the supercharger at the same time.Search for the noise on utube and look on ebay for the parts to fix or zzp.

This!
Easy Fix. It is plastic. I guess it is in case something locks up, that way you don't break everything. The get loose as they age.
stock coupler
aftermarket coupler

Those links say that the coupler noise is only at idle. Mine is only at 1,900 rpm.
 
Right, this is my third supercharged 3800. When the coupler goes you will hear it above idle. It will do it a weird times depending on load and engine temp.
 
Originally Posted By: ls1mike
Right, this is my third supercharged 3800. When the coupler goes you will hear it above idle. It will do it a weird times depending on load and engine temp.

Cool. It's a cheap fix, so I guess I don't have much to lose. Is the aftermarket coupler worth the extra price? I run a stock pulley and don't plan on going smaller.
 
I used it in mine buts its modded.For 10 more bucks its peace of mind at the least.I got the coupler and oil from zzp if you get it from GM you need two bottles, they ZZP) have it measured out already.There are kits on ebay as well.
 
An hr for a tech. No nothing special, getting the old oil out is the hardest part.And you have to use a non hardening gasket maker on the nose at least that's what they recommend.
 
Well, it's not the supercharger coupler!

It started off pretty doubtful as there was no back-forth wiggle in the pulley. I pulled the nose cone off last night and the old coupler was in great shape with no hole disfiguration. In fact, it was on there pretty snug and I had to pry it off to put the new one on (I had already purchased and received it, so why not?). I was not able to get a good test drive in last night to get everything up to temp, but this morning I have confirmed that the noise is still there.

Could this be a bad water pump? The pulley seems to have a bit of wobble while the engine is idling but I did not try moving it by hand while I had the belts off. The current unit is a Bosch that has been on there for about 9 months and 10,000 miles (still within the shop 12 month/12,000 mile warranty!).

Whatever it is, I will be taking it in for diagnosis on Wednesday (shop is booked today, closed on weekends, and I will be out of town from Sunday afternoon through Tuesday evening) and will update this thread when I know more.
 
The shop says it is an internal issue with the catalytic converter (breaking up?) and the resonator(something loose, maybe a piece of the cat?). I think there has been something loose in the resonator since I first bought it or shortly thereafter, but the cat issue is new.

I will continue to drive it as-is, but it sounds like a good excuse for a full aftermarket exhaust system!
 
Originally Posted By: NMBurb02
The shop says it is an internal issue with the catalytic converter (breaking up?) and the resonator(something loose, maybe a piece of the cat?). I think there has been something loose in the resonator since I first bought it or shortly thereafter, but the cat issue is new.

I will continue to drive it as-is, but it sounds like a good excuse for a full aftermarket exhaust system!

Check your smog laws before replacing the cat. Some areas need the premium California approved cat.
 
what makes you so sure that it is indeed NOT coming from the shield? that seems to be the most likely origin of that noise. how have you eliminated hat source?
 
Originally Posted By: artificialist
Originally Posted By: NMBurb02
The shop says it is an internal issue with the catalytic converter (breaking up?) and the resonator(something loose, maybe a piece of the cat?). I think there has been something loose in the resonator since I first bought it or shortly thereafter, but the cat issue is new.

I will continue to drive it as-is, but it sounds like a good excuse for a full aftermarket exhaust system!

Check your smog laws before replacing the cat. Some areas need the premium California approved cat.

It is a CA registered car, so it does need a CA compliant cat, even though the emission system is a non-CA Fed system. $1,100 from the dealer or $600 for a Magnaflow.
 
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Originally Posted By: Vikas
what makes you so sure that it is indeed NOT coming from the shield? that seems to be the most likely origin of that noise. how have you eliminated hat source?

I had it checked out by a shop I trust. Their first thought was a heat shield, but they ruled that out. They also recommended driving it as-is until it gets worse or throws a code, so they are not just fishing for extra work.
 
You can lightly tap on the converter with a rubber mallet, and will probably hear the noise. I had a similar issue on a '97 Dakota. I had an aftermarket/universal converter welded in for $300 and honestly, the truck ran a ton better after that. It sounded much better as well. Good luck!
 
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