Thread: Rapping/Rattle at Idle, goes away when revving

Hi folks. I have gotten some help here before, and am hoping to get it again. I have a 2000 GTP, 3.5 pulley, CAI, stock other than that, 139k, needs an oil change but not low on oil. Last weekend I changed my battery, and yesterday it rained really hard, these are ust a couple recent variables to the car. Yesterday driving home, it developed a bad rapping sound/rattle kind of knocking sound at idle, as soon as you get over 900 rpms it stops, and doesnt come back til falling back to that range. I have no check engine light on, no smoke, and the car runs exactly as it should. I even got it on the boost to make sure and it was fine. I really don't know if this is internal or not, but I feel like I can hear the internals of the engine running seperately from this sound. The sound certainly seems loudest on the pulley side of the car. Also when it starts, it sounds like something might be catching or something like that. My gas milage has always been kind of crappy so nothing major changing there. Any advice? Thank you in advance!

Alright, going to see if I can find a shade tree mechanic to do it, I don't have the tools here...Thank you for the tip

So I have not had a chance to take the belt off yet, but using the skill I do have I have figured out that I am almost 100% sure it is some kind of bearing /pulley issue. As soon as I clicked on the AC (Something I havent done since I heard the noise the first time) the noise quieted. Something is making a rapping sound unless it has tention on it basically. Any tips from here?

put stock pulley back on its prolly your motor knocking... or a bad supercharger coupler

The car has had that pulley on it since I bought it, I forgot to mention it does have a performance edu as well. It has never been an issue. I do not think its knocking, because the sound is not at all in time with the sound of the internal engine movement.

I am not very car savvy, but a family member had this issue with a park ave and it was the AC Clutch, not sure if its relevant to this or not just trying to help.

When the engine is running, take a long screwdriver and place it against the s/c snout. Take the other end (handle) and place it against your palm while your ear is resting against the outside of your hand. You will be surprised what you can hear using the screwdriver as a conduit.

My guess: bad supercharger pulley.

When mine was worn out (120k miles), it sounded like rocks were tumbling inside my engine. I could only hear at idle. It was so bad that I was sure the needle bearings were trashed. When I cracked it open (took the lobes out and everything), the only thing that was bad was the pulley.

The car has been whisper quiet ever since replacement.