Thread: Strange rattle/knock

I'm not sure 100% if i'm posting in the right area but I will give it a shot anyway. Past few days I've noticed a strange rattle/knock coming from the front of my car. Now it only happens then the car is in drive with my foot on the brake at lights and or sitting in my driveway. When I put the car in Reverse, Neutral and park it doesn't make the noise. When I accelerate the noise goes away and the car runs and drives fine. It's a 2000 Grand Prix GTP with 140,000 miles on it today. As far as history of underneath goes I have replaced the main motor mount as well the passenger side Axle as well 4 brand new wheel bearings around the car. Everything else on the car is pretty much stock except for the intake. And the original Trans mount is still on the car as well the original Driver side cv axle is still on the car as well. Any help would be greatly appreciated and if posted in the wrong section i'm sorry. Thanks guys

Could be something just rattling once the rpm's drop. It may do it in drive but not reverse because the engine slightly rocks forwards or backwards. Can you have someone put it and drive while you look? Or just use the parking brake.

kinda sounds like the sc coupler has gone bad on you.

take the sc belt off, then turn the sc pulley back and fourth, kinda snap it back and fourth, if you feel slop thats the sound, kinda sounds like rocks in the sc. its easy to replace, costs about 50 bucks or less.

you'll only hear it at idle too, in gear or in park.

search you tube theres a few how to vids.

I was thinking that too on the sc coupler I mean 140,000 original everything mind you it was babied by my mom and dad when they owned it before I got it from them. But would a bad coupler make that much of a noticeable knocking/rattling. I had it at my mechanic's yesterday I had dropped it off the night before to have him look at it (family friend). And they said everything seemed ok to them and there was nothing wrong and the engine seemed like it was solid. I was more worried about a rod knock which he was like no man this engine is still in solid shape for having this many miles.

taking the belt off is free. see if the pulley has play in it.

at 140,000 id think the coupler is shot. really dont matter that it was babied, they wear out.

buy a green one on line or zzp, used GM supercharger oil too. (and anabolic sealer? ) ill never spell the name right for the sealant you use for the snout back to the case. some one will chime in and name it properly. lol


when i was buying my car, i took it to a shop for a inspection. he had no idea the coupler was bad, and called it a bad supercharger bearing, i knew a bit better. used that info to get even more money off the asking price. it was the car lots mechanic and they let me under the car and showed me every thing that was wrong. so his words went to me and the salesman at the car lot.

So you don't think this could be tranny related or anything ? I've really never had an experience with a bad coupler I have read they sound like rocks rolling around but in drive at a light they can cause that kind of noise ?

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it sounds horrible lol it was one of the first things i fixed on my car.

not being there driving or hearing the car, no one could be 100% of any thing, but it does sound like a coupler.

like i said, its free to check it. hell, take the belt off, start the car up. if the sound is gone. its the coupler.

I'll pull the belt off tomorrow after work I'd do it now but it's getting dark here in cleveland. But I did go out there and listen and it does seem like there is something going on over there by the base of the supercharger. I was just freaking out because this car is supposed to go in in 2 weeks for a fresh coat of paint and all the body work in the world to be done to it as well went ahead and picked up another block to get cracking for the winter overhaul of this car and my camaro.

Do u have a fwi I had one and in drive it would only rattle then I added rubber house to the housing and boom fixed

Well because I didn't want to remove the computer off of the original housing it sat on I pretty much left it there pulled off all the rest and modified it a bit so it could rest there. Now I'm starting to think could my Filter be smacking the plastic. Fwi your referencing intake right ?

fwi= fender wall/well intake.(whatever) filters in the fender. his intake pipe was tapping the fender it seems.

Yea I just went out and checked mine and it clears. Just weird, Drive with foot on brake it thumps when I start rolling it goes away, neutral and reverse no thump.

post a vid if you can. if you can hear it loud enough to record it.

maybe a heat shield is loose?

Yea could be that too. I just couldn't see a coupler making that kind of a thumping noise inside the car unless they really are capable of causing that kind of a vibration/thump

One thing as well could this be a Trans mount issue ? because the motor mount is in there secure and has 2,000 miles on it could the trans mount cause a nasty thump while sitting in drive ?

I could be very wrong here but I recall reading something about a flex plate issue. Mine has the same kind of thump to it sometimes. It doesn't do it all the time.

I was hoping someone wasn't going to say flexplate.

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flex plate would be heard form the drivers side of the engine. if you get the car up in the air and get under it you could hear it better should it be the flex.

I listened to a bad one on YouTube and it definately didn't sound like that. I'm going to run it to my buddies shop Tuesday and see if something's rattling or if the mount is shot. And I've already ordered a new coupler kit just because 140k she's up there in miles on the original blower. Wouldn't hurt to swap that and I'm also thinking the driver side cv could be the issue too

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Here's a question for you guys. I noticed today when I had the hood up looking through the windshield that when I put my car in drive the upper radiator hose shakes like crazy it seems. As well I have noticed it has also been running a bit hotter than usual lately as well. A little while ago this car never really climbed past the mid mark now it seems like it has been going past this area now. Figured I'd ask a lot of you guys know these cars well.