At low rpms and even high gears everything sounds fine. However, when i accelerate hard or am at high rpms (past 3000-3500) I hear a weird rattling sound coming from the back passenger side of the car. Almost like the exhaust is vibrating against something. The drivers side/exhaust sounds fine, no problems there. Also it doesn't sound like pebbles in the exhaust or anything like that. The sound is especially bad in 2nd gear. I checked to see if the exhaust was loose or if one of the ties had come off but it doesn't seem like that. Any ideas?