I have a 2004 V8 Sport with full time AWD. Just turned 80K miles. Bought it used last year. I thought the tires needed to be changed because of a roar I was noticing. No real vibration in the steering and ride felt fairly smooth, but the tread looked worn so I got new tires. The roaring is still there. This is my first full time AWD vehicle. IS there a maintenance I may be missing for this type of vehicle for the drive train or could it be wheel bearings? Any ideas? Thanks.