02 Z28 M6
I have a rattle noise at low rpm, can hear it at idle, when you rev up engine you can hear it as idle comes back down, sounds kind of like it is delayed, idle drops down then you can hear rattle sound drop down, about 5 people have told me it is not a lifter tapping, anybody have a clue what it could be???

 

Sometimes these Tremec tranis will rattle or growl at idle. But it could be any ine or two of a million different things. Maybe a heat shield.

 

some thing to worry about?mine rattles abit a idle not much.

 

I notice that you have a catted Y-Pipe. Could it possibly be the cats coming apart?? Most of the time when there's enough exhaust flow, they don't rattle. It's when the RPM's start to come down and the exhaust flow drops that they'll "flutter" a bit.

 

I thought about the tranny myself, kinda sounds like it, I don't have any cats, I have the complete hedman header LT's and matching Y pipe and cat back exhaust system. Car seems to run just fine, very strong, just can't figure out where noise is coming from. I thought maybe the tensioner or idler pulleys but they wouldn't be delayed at all in sound, I doubt it is the water pump, but who knows, maybe it is

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2002 Z28 M6
Hedman LT's, Hedman ORY, Hedman cat back, SLP lid, K&N, VR velocity stack