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

I took the car for a fast drive on a freshly resurfaced four lane and the noise I was describing is gone. It is hard for me to believe that brace was responsible, but replacing the bolt was the only change I made on the car.

Even with the brace loose I was unable to move the exhaust around much at all, but apparently once that brace was secured what ever the cause was vanquished.

It was worrisome having to listen to that unidentified noise during that 1200 mile trip.

Thanks to everyone for your suggestions.

Randy

Time to replace you axles// C/V joints. 267 k is a lot of miles. What your hearing would be the slack created by the grooves worn into the ball track in the C/V joints. When you let off the gasoline pedal, the ball bearings just float until you give power to it. Then they click as the axle turns. Given your miles on the car, I would think axles. They sell nice rebuilts. Jacking the car up and running the wheel with engine On is not a good way to test them. Extreme angle of the C/V joints can give a false good. Good luck and let the brickboard
Known the results.

760's, 960's and the FWD Volvos have CV joints, 940's (except for the early 1990's SE's) don't. They don't have an IRS. They have a solid rear axle like a 240.

Sounds like a driveshaft or motor mount issue to me.

Hi Randy,
I had an annoying noise appear out of nowhere similar to what you describe. I tried slackening the bolts at the front of the prop shaft, cant remember if i changed its position as it was a while ago, but the noise disappeared so you may be on the right track there.

Regards
Pierso
1993 2L turbo estate

"... there is no contact between the pan and the rubber the space is only about 1/8"..."

It sounds like the motor mounts may be near their end of life. Is the cooling fan contacting the lower arc of the shroud, or do you have an electric fan mounted directly to the radiator?
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Find a shop that has some - chassis ears - a device that has several microphones and a receiver. They are used to find chassis squeaked and such. They do not get used too much, perhaps you can rent them. Looks like they cost about a hundred bucks. Try ebay.

You could take a length of garden hose and tape the end at various locations, run it up through a window and listen to the other end.