Our wagon has 175K, mostly highway miles. The car developed a drone, almost like wind past your window during a winter storm about two months ago, Per the board, we had the center drive shaft changes - no change. The drone is getting louder. When goinig down hill, if we put the car in neutral, the drone stays the same so we think its not the tranny - car shifts smoothly. Any additional input would be helpful, also, do people just keep driving these cars with this kind of rear end noise ? Two mechanics here in Portland, OR have not been able to find the cause - " just play the radio louder " is getting harder to do as the noise keeps getting louder ! Thanks is advance