Motor noise 99 Grand Prix 3100

[JASON 77]

Have a 99 grand prix there is a knockin noise from the motor, but not a rod. have heard other 3100 vehicles with this noise, could it be timing chain, lifters. kind of sounds like a rod knockin but it is not it. at idle pretty loud, raise the rpm's to 2000 or above gets quiter. have checked the torque convertor bolts, changed oil. i do not know what else it could be, but some say these motor are common for this noise . any/all help greatly appreciated.

Jason

[bszopi]

Is the noise only there when the engine is cold?

[IsaacHayes]

Piston slap or timing chain slack. Mine made the noise for years, then I replaced the timing chain when I had to replace the cover gasket. The noise went away. When it's really cold you can hear a slight noise still under the car (piston slap) but once it warms up you don't hear it. The loudest noise I hear now is the injectors firing.

[19Cutlass94]

Once the car warms up you shouldnt hear it. If you do theres deff something wrong other than the norm

[JASON 77]

it does it cold or hot. it definetly is not a rod or main knock. it kinda sounds like loose torque convertor bolts but they are not. i am stumped.

[19Cutlass94]

Where does it sound like its coming from?

[Chris88CL]

Piston slap for sure. 99 was a terrible year for it from my experience. My pistons were VERY worn.

[19Cutlass94]

was a problem with the pistons or the rings? that makes it do this? Cause mine does this when cold, but once warm the noise goes away... I always thought it was the rings

[bszopi]

Its the pistons. GM's explanation for is this: The pistons are at the minimum tolerance and the bore is at the maximum tolerance. Therefore, before the components heat up and expand, there is room for the piston to "slap" around inside the bore. Once the engine heats up and the components expand, the tolerances are closed up and the slap goes away.

[snowblindburd]

Does it sound anything like this?

Videos: The ones without links will be uploaded after my class today. Or I will try to at least. It's not looking good for the tranny or my engine mounts. Exhaust sounds great though.

Right after startup, regular (I assume!?!) engine noise and then as I pan over you can hear the knocking slightly:
Startup - Cold Engine




Video two, under car. Car put in drive, knocking, then at 17 seconds put into neutral and revved. knocking at 1000-1200 rpms:
It doesn't sound good..

In engine bay doing pretty much the same thing. And wow I think I need new engine mounts...:
Engine Bay

Exhaust, I don't hear any bad noises here:
Exhaust

[Azrael]

I heard after a certain year GM stopped matching piston sizes to what I assume is the block cylinders. Don't know how true that is but it would explain GM's sudden issues with piston slap.