Odd noise on acceleration only when in gear - help diagnose? [Archive] - GrandAmGT.com Forum


View Full Version : Odd noise on acceleration only when in gear - help diagnose?

03-08-2005, 07:20 AM
Hey guys, just thought I'd post a problem I'm having with my car here and see if anyone knows offhand what this could be. First off, the car seems to run fine, although I may have an external LIM leak (hey not bad for original LIM gasket at 80,000 miles! :rolleyes: ). There's no slipping in the transmission though it does not shift as tight as my sisters car with 40k on it.

Anyway, it's developed an odd noise that I would describe as a rattle or what you might hear with a leaky exhaust manifold gasket. It's not popping noise, but more of a rattle.

The noise occcurs when applying throttle in gear. In park, or neutral while rolling, I can rev the engine and it sounds perfect. In gear though, I hit the gas and it sounds like an '86 cavalier with a leaky exhaust. (I shouldn't be stuck on this exhaust thing as it might not even be exhaust related...)

When coasting in gear the car sounds fine -- it's only when applying throttle. A little throttle the noise isn't as loud. Floor it and it's more pronounced. Also, at a stoplight in Drive if I hold the brake and apply some gas I get the same noise. (So that rules out differential, right?)

So I'm thinking and I came up with a list of the following things that could be wrong:

1.) Exhaust manifold leak that only becomes present under load
2.) Loose heat shield that rattles when transmission is engaged.
3.) Torque converter
4.) Other transmission problems
5.) Does a leaky LIM make noise under engine load?

Again it sounds fine in park. I was cleaning my car this weekend and started it up and pulled the throttle on the egine hopeing I could find the sound...but I couldn't hear anything. Throw it in drive though and it's noisy.

I'm really hoping this isn't a transmission problem...I'd hate to be pulling the engine and replacing a trans...but I'm worried it is. I just hope this damn car holds out so I can unload it once 5spd 2005 Mustang GT's are more readily available (and maybe discounted rather than priced a few K more than MSRP!!!). Not that I don't like my car, I'm just worried after 4 years and 80,000 miles my thusfar troublefree car is gonna have the you-know-what hit the fan for all those problems that didn't develop early on like most others cars. (i.e. lim, wheel hubs, transmission, window scratches, etc etc etc...)

So any help would be much appreciated. If you want I can probably toss my video camera in the car tonight, go for a spin, and try to record the noise.

03-11-2005, 08:41 AM
Well I'm going to be looking over it this weekend, probably tommorrow. I'm thinking maybe this is actually a minor exhaust leak.

So if you have a minor leak, will it sound fine with no engine load, but with a load will there be increased exhaust pressure that could cause the sound?

Anyone have any ideas or is this something no one else had dealt with?

03-21-2005, 01:10 PM
UPDATE: It's an exhaust leak somewhere behind the engine that only really makes noise when the engine is under load.

It's either the rear manifold gasket or the connection to the downpipe. I'm not really sure, it's hard to get close down there with the engine running.

Oh well, now I gotta decide...fix it myself, take it to a shop, get headers...hmmm...