Engine noise (knock) on startup.

[Lazerred1]

My 97 Chevy PU with 70,000 miles just had the oil changed from synthetic to dyno (mechanic did it when some seals were replaced) and now have what I can only describe as a knock on startup which continues for maybe 2 minutes. Really sounds like a diesel. It did it somewhat with the synthetic, but not as bad or as long. It had Pennzoil Platinum 5w30 and now has Castrol 10w30.

Think this is oil related or something else? Good deal at O'Reilly now on PP, basically free with rebate or I have some Castrol 0w30 Euro I could use. Suggestions appreciated.

 

[mechtech2]

Try the simple things first.
It probably is an oil filter that does not have the proper anti drain back valves in it.
Good luck!

 

[Lazerred1]

That one I hadn't thought of. I think I have an Amsoil for this vehicle laying around. I'll try that.