Strange Sound. Any ideas?

[JoshCorlin]

So, My car makes a weird "thunk" sound when I don't give it enough gas when disengaging the clutch at a stop light. I know it's not engine lug because it's only one solid THUNK, then its gone. It's not super loud but you can definatly here it from inside the cab.
It also does it when shifting under heavy acceleration or from a launch. I thought at first that it might be one of the motor mounts going out, causing contact when the engine troques up, but they all seem fine. Also, the axles aren't clicking and show no signs of damage to the boot, so I don't think that they are the problem. The clutch system seems to be working fine also, so I have no idea whats going on.
I'm building an engine right now and want to try to figure this out before I pull the old motor out and throw in a more powerfull engine with an upgraded clutch. I don't know if it will help, but it kind of sounds like it's coming from the tranny side when inside the cab. It's not causing any driving problems, but I know that NO sound should go over looked with DSMs.

 

[blowinsmoke95]

upgrade to poly motor mounts... replace lower control arm bushings, and get some new struts, thats the best things you can do for it...

 

[JoshCorlin]

upgrade to poly motor mounts... replace lower control arm bushings, and get some new struts, thats the best things you can do for it...

Well, hmmmm, okay?...... Struts are pretty new KYBs, and it has an Eibach camber kit, so if it were the lower control arm bushings, wouldn't that cause some seriuos handling problems and crappy ride. The poly motor mounts would be somthing to look into, but I heard they cause a lot of engine vibration.

 

[Mizzat508]

Sometimes when I drop into 2nd from first, i'll say under accel but not like crazy, 4500+ rpms, it thunks a bit. I think it's just my tranny needing a flush (145k), but if its something to do with my clutch....it sounds SIMILAR to what you described when shifting. Also, i went to start my car when I got out of school yesterday and it made an aweful grinding noise. It sounded as if the starter was just grinding against an immobile flywheel...i released the clutch and depressed it again and it started fine. It hasnt made the thunk though.

 

[JoshCorlin]

My car never made no crazy grinding sound......ever, and if it were a suspension problem the sound would be constant. You would here it with every bump on the road or under acceleration or decelleration. It's only happening under load from a stop or fast, high RPM shifting. Any time else, nothing.WTF