I recently experienced a louder than normal drive train caused by two separate, though similar, situations. When I blew the right rear tire at 16K miles I replaced it with a new Bridgstone of the same type and size. Apparently there was just enough difference between the circumference of the new tire compare to the slightly worn tire on the other side to cause the differential to slip and make noise, especially under decelleration. I had just had the tires rotated, but moved the rears to the front, and this silenced the rear end. Then, last week I noticed the same noise again. Friday morning, while doing my normal pre-flight walkaround, I thought the right rear looked low. Sure enough, it read only 17 lbs. I pumped it back up to 37, and took my tire gauge with me to check it at work. Unfortunately, a check engine light just a quarter mile down the road (O2 sensor) convinced me to leave the VX home for the day, but it was quiet for the short time I drove it. I found a screw in the tread this morning, which turned into a big leak when removed. I put a plug in it, so it should be fine now.
It has been mentioned many times about not running the spare on the rear, but even a small mismatch can result in a noisy rear.
Gregg
2001 Proton Yellow #1379