Thumping noise in 99 grand prix gtp


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Thumping noise in 99 grand prix gtp

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tfortney
New User

Jul 26, 2011, 8:30 AM

Post #1 of 5 (3434 views)

Thumping noise in 99 grand prix gtp	Sign In

I have a 1999 Pontiac Grand Prix GTP with the 3.8 liter supercharged V-6 with 118K miles on it. I was trying to make a light and hit a serious bump in the road which gave the car quite a toss. Tires were fine a little scraping under the front body but not to frame or engine parts. After parking it for about an i started it up and checked to make sure all fluid was fine and no leaks. it all checked good. once i began to drive it i could hear a thumping sound upon acceleration but the sound would go away once i reached about 20 miles an hour or took my foot off the pedal. I will say that again if i took my foot off the pedal at any time the sound would go away. the only other time i heard the sound was when i jump on it on the interstate and it would only be until the shift was through.

any thing will help here. i am pretty car savvy and would love to be able to fix this myself and diagnose it without having to take it in.

Thanks

(This post was edited by tfortney on Jul 26, 2011, 2:15 PM)

Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jul 26, 2011, 4:53 PM

Post #2 of 5 (3422 views)

Re: Thumping noise in 99 grand prix gtp	Sign In

Where does the thumping noise sound like it is coming from? Does the noise intensify or does its timing change as your speed increases? Noises are hard to diagnose without actually hearing them.

You might want to get the vehicle in the air and inspect for damage.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

tfortney
New User

Jul 26, 2011, 5:54 PM

Post #3 of 5 (3413 views)

Re: Thumping noise in 99 grand prix gtp	Sign In

sounds more or less like it is coming from below the passenger seat. it increases as speed increases but only up to about maybe 20 mph. then starts for a second if i floor it. i will have to get it up on a lift to see how the damage looks. would a tranny problem cause that sound?

Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jul 26, 2011, 6:07 PM

Post #4 of 5 (3406 views)

Re: Thumping noise in 99 grand prix gtp	Sign In

Hopefully not. I really haven't heard a transaxle make a thumping noise before. Once in the air, you might be able to see if there is some damage. Maybe an exhaust part is touching or a broken mount that is causing the engine to lift up and throw the CV axle angle off is causing your noise. Those are just guesses.
Let us know what you find out.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jul 26, 2011, 6:08 PM)

tfortney
New User

Jul 27, 2011, 12:20 AM

Post #5 of 5 (3396 views)

Re: Thumping noise in 99 grand prix gtp	Sign In

thanks will do. hopefully i can get it up on a lift this week

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