I have a grinding noise in my 2000 S70SE.. seems like its coming from the rear..doesn't change pitch when speed changes but seems to come on at about 30 mph..some times its louder than others and rarely it doesnt happen at all... in bad snow it sounds like a grinder running in my back seat.. .Took it to a dealer a number of times but they couldn't find anything.. anyone know of problems with axle's or breaks that would cause this.. It doesnt increase/decrease with speed and doesnt go away when breaking...just always there and worse in bad /cold weather..I'm thinking maybe an axle bearing?