My 1988 Volvo 240 wagon 246,000 miles .suddenly started making a high pitch noise when hitting +30 MPH yesterday coming home from work. There is no noise when the car is idling, or in park. The noise decreases a little when Im cruising at about 60 MPH. When I take my foot off the pedal, the noise get really high and slowly goes away as I hit the brke pedal. The car's been running good. the only thing I did lately to the car was rotate the tires but that was 2 weekends ago and changed the front brakes 2 months ago, oil change too. Anyone have an idea what could be causing the high pitch noise.

 

Auto or man

 

Automatic w/ od

 

It might be the center support bearing or low ATF (the torque converter will make noise).

I would start by checking the transmission fluid:
https://customers.volvocars.com/owne...0_03b.htm#pg68

 

I was going to say it sounds like the differential is getting worn due to a lack of oil, but the sound should go away once you let off of the gas. Might be a good idea to check the fluid anyways.

 

I checked the transmission oil before leaving work and it was within the cold temperature range and still looks good. there is a very very minor leak but it hasn't affected the transmission as far as I can see. Now where is the center support bearing located at?

 

It's under the center of the car, where the front and rear driveline meet. Is the noise below the shifter or somewhere else? Does the noise go away when you coast in neutral?

For me high pitched noise has always been something with the brakes. With driveline and wheel bearings it can be hard to pinpoint while driving.

 

I have a 92 240 wagon that does the same thing. Checked and packed wheel bearings but didn't think about the center support....thanks for the idea.

 

My guess would be the center support bearing. The real test is to put the car in neutral when cruising at 50+. If there is no change to the pitch of the whine from when there is a load on it vs. rolling in neutral then that would be the culprit.

If you DO hear a difference from a load (accelerating/decelerating) vs. a no-load (rolling in neutral) condition, then I would suspect a problem in the differential.

Good luck