Thumping Sound
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Teching In
Joined: Oct 2019
Posts: 2
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From: Houston Texas
Thumping Sound I have an automatic 98 Trans Am, 109k mi on it, that hasn’t been ran in a little over a month. Started it today and everything was normal until I put it in drive - there was a loud, constant thumping/pulsing noise that sounded like it was coming from the engine area but I could feel it shaking the pedals a little as well. I parked & let it warm up fully before taking it around the block again, and then the thumping was still there but it was a lot lower and subtler. The thumping gets faster with RPM but only in drive or reverse - it’s silent in park and neutral. Anyone experience this as well or know what might be wrong with it??
My first thought would be something behind the transmission but if you say that it is related to RPM and not speed, then I would think it is something inside the transmission, which would be weird.
Have you tried coasting (with the car moving) and shifting in to Neutral? Have you stopped the car and given gas to the engine in Park and Neutral?
Have you tried coasting (with the car moving) and shifting in to Neutral? Have you stopped the car and given gas to the engine in Park and Neutral?
Thread Starter
Teching In
Joined: Oct 2019
Posts: 2
Likes: 0
From: Houston Texas
I revved it up in park and neutral but no noise at all with that. I listened to it a little more and the best way I can describe it is it sounds like knocking on dense wood - also I think it could be speed instead of RPM related now (but not 100% sure), because I got it into 2nd gear this time and right after the shift it was pretty loud and fast still.
The sound makes me think its in the driveline. If so, you probably don't want to drive it very long like this. Something is probably loose in the rear end or on the drive shaft. 
To confirm, I would listen at a shift point. Drive to 20 mph or so and then shift into Low gear, keeping gas into it to maintain your speed. Your RPMs should shoot up and if the frequency of the sound doesn't change much, then you'll know it's behind the transmission.
To confirm, I would listen at a shift point. Drive to 20 mph or so and then shift into Low gear, keeping gas into it to maintain your speed. Your RPMs should shoot up and if the frequency of the sound doesn't change much, then you'll know it's behind the transmission.
