I have a 2004 XC70. I recently replaced the Pirelli tires with the slightly larger Yokohama Avid V4s (contrary to the vehement advice of the dealer). Since then, when I drive in the rain, I occasionally get a very loud humming sound or tone, like a higher-pitched dial tone, or a kind of loud grinding sound. Does anyone have any idea what these could be? I hate to ask the dealer, because I'll just get another lecture on why I should have bought their $200 Michelin tires! Thanks!

 

It's not the tires, I have a 2004 with the same tires on it. Do some searching, there is a know issue with the exhaust contracting from the cold water and rubbing against the drive shaft. The exhaust can get close to the drive shaft if the car has bottomed out and the cross brase (look under the car about middle front to back) is hit pushing the exhaust close to the drive shaft.

Check out swedespeed.com or volvoxc.com for a better answer.

 

The noise is in fact the muffler rubbing against the driveshaft. Your local dealer has a new hanger kit they can install to remedy this problem. If your car is under warranty, they will do it free of charge. If it's not, I don't think it costs very much to have it done.