03Outback

I have a 2003 Outback. When I accelerate at a dead stop there is a awful vibration sound and it continues all the way up to 45 mph..when I'm cruising at 40mph or 70 I can hear sputtering exhaust sound... Any solutions?

I have access to seatbelt material... How do I restring/replace a Front Passenger Seatbelt.. I attempted to take the bolts out and found out the winding mechanism got locked up after frustrated work got it back in place but still need to replace the belt..I called a dealer and they wanted $550....to much for me... any help? Thank You