I recently had bbk shorty headers and a bbk x-pipe installed on my mustang. After driving it around i noticed a pretty loud rattling sound coming from underneath the drivers seat. I thought that the x-pipe had come lose and that it would be a simple fix. However i found out that my transmission mounts were shot, and that the transmission was moving and coming into contact with the x-pipe and that was what was causing the rattle. I was told that there was plenty of clearance for both the headers and the x-pipe and that the only reason for the rattle was the transmission. I got the transmission mounts replaced and I though this would be the end of the problem, but I was wrong. The rattle does not occur as often now but is still noticible from time to time. I mainly hear it now when I go over bumps in the road or during fast acceleration. If it helps I have an automatic transmission in the car. I really have no idea what could be the cause of the rattle now, and I was wondering if anyone here could help me out with this. Any advice will be useful.

 

check the motor mounts. when you accel, the motor torques sideways and backwards. this can move the exhaust into the body. and check that all the exhaust hangers are used. one thats off the mount can knock. and check for any heat sheilding thats loose. that rattles too. just some ideas.

 

Most likely the culprit. When I installed my X-pipe I must have accidentally knocked one of the hangers out on the muffler, but my noise was coming from near the rear axle, at least thats what I thought until I got under it.

 

Thanks for the suggestions. I am going to chech out the problems that were mentioned, and hopefuly be able to fix the rattle and get the car sounding the way it should.

 

the rattle is probably just the noise the x pipe makes. it's how they sound. really tinny noise.

 

It's not the first time I've heard people say that so I think it really depends on your muffler. My exhaust doesn't sound "tinny" at all to me.

 

I can't hear the rattling/pinging unless I hear the echo off of a high curb or a wall. it sounds like it's coming from right under the driver's seat as well.