Alright I'm a fairly new Volvo owner but I purchased an 86 wagon a few months ago with 200,000 plus miles on it. It is in good shape and starts, run, idles fine. Something weird though is that when im driving it makes a weird sound that appears to be coming from the bottom of the engine or tranny area. It's almost like a loud vibration or maybe a grinding type sound It doesn't happen when it shifts or when I stop or accelerate but at intermittent low speeds up to about 50 mph. If i speed up or slow down when it starts it goes away. It's kinda loud though when it echo's off the pavement. It doesn't appear to effect how it drives. If anyone has any clues please help. Nothing underneath seems to be loose either. Thanks in advance

It could be heat shields on the exhaust system?

Center support bearing is a good guess, though that usually shows up most on acceleration. The heat shield (i.e. sheet metal) around th4e front pipe is another good guess. I agree that if the shield is loose, you can remove it, and no ill effect will come to your car.

Another thought I had is perhaps you have a hanging rear brake caliper. I say rear, because if it was a front, your car would probably pull to one side. And going with the drive train therory (which is indeed most likely), you could also have a trashed rear end, though that is not as likely as some of the other suggestions. Allen

I would start by checking the center mount and bearing on the driveshaft. I had a similar noise not too long ago and that was it.

Is this sound related to engine speed or road speed? Is the sound changed if you put the car into neutral?

It's a little hard to tell from your description, but it's possible you've got a driveline problem. Get under the rear of the car with one side jacked up, and give a good push-pull at each U-joint to make sure there is no play in them. Also, squirt some WD-40 in the center support bearing and see if that has any effect at all on the sound. If it stops the sound, it will only stop it temporarily, and if this is the case you should make plans to put in a new bearing & rubber mount.

Another thought is totally unrelated: it could be rattling of the sheet metal around your exhaust front pipe, if you still have it. When the engine is cool check to see if any of the sheet metal is loose. If it is, rip it off in whatever manner you have at your disposal. It's totally unnecessary.