1994 944T 267K

On a recent interstate trip I became aware of an annoying noise at speed.

It is a rapid vibration like sound not unlike what would be the sound of the exhaust system hitting chassis or body pan. I would guess the rate to be about four times a second. It is not strong enough to actually create a vibration that can be felt in the car.

It is evident when maintaining a constant speed or when accelerating. Back off of the accelerator even the smallest amount and the sound goes away.

I put the car on stands today and have convinced myself that it is not the exhaust system although I did find that the brace that goes between the back of the transmission and the exhaust pipe was missing the fastener that attaches it to the exhaust pipe just ahead of the converter. I installed a replacement bolt.

I removed the transmission mount for inspection and while it is a little soft it is not broken or torn. Grasping the rear of the transmission and trying to move it around did not result in much flexing or movement.

I took the plate down that the center support bearing attaches to so I could get some movement on the driveshaft and the universal joints but nothing was revealed.

Trying to rock the engine left and right did not reveal a lot of movement. There is a "rubber bumper" that fits between the cross member and the oil pan and while there is no contact between the pan and the rubber the space is only about 1/8".

I would guess that perhaps the missing bolt was the source but I haven't taken off of the stands yet and taken a drive. Before I do does anyone have a suggestion of where else to look?

Randy