While driving home late last night on a deserted interstate, noticed my 97 Brighton Wagon(AWD, 158,000 miles) making a notable deep noise, coming from somewhere on the RHS of the vehicle. Couldn't tell whether it was front or back (just me alone in the car). It did seem to vary a little according to my speed, increasing with speed,, and also quieted and increased somewhat on its own at times, all while going straight. Within this general deep noise, was at times an occasional muted thumping sound - as best I can describe it - but I felt nothing. Noise may have been around a while - I just ran out of radio to listen to last night and that made any car noise more audible. It was pretty alarming to hear although in the course of 130 mile drive it didn't worsen, just got softer and louder.
I'm not a DYI'er (beyond oil and air filter changes) but am trying to figure how to proceed. My WA guess is the noise could be drive shaft or even something from the exhaust system itself and the latter might be easier to find on examination. Suspension?
I know that even experts hearing a noise can't always determine what it is.
Any suggestions as to possibilities and as to how urgent it might be? I don't want t spend a fortune on something that could be noisy for
10,000, 20,000 miles, or more, but not risk failure. Although the current plans are to keep this car UFN.TIA