i just installed a 2.5 alta catback on my 05...when i take off in 1st gear im getting a rattle and sort of a knocking sound comming from under the front seats...any ideas and possible fixes for this..??? thanks for your help!!

 

If you didn't cut some of the underbrace where the resonator hangers are that's probably it. I had a similar problem to yours and had the under plate cut to allow movement of the resonator, otherwise the resonator would hit the plate and it made a really annoyingly loud vibration sound.

 

ya I figured it out. I didn't cut it how ever I just took a pair of vice grips and bent the little lip down to allow clearance.

 

edit: nevermind

 

thanks for looking tho!

 

I had a very similar problem.

I had the B&M short shifter installed (which lowers the shifter housing about 1" into the exhaust channel) and the Alta 2.5 cat-back. The resonator that came with the Alta was so large that it was trapping the heat shielding between the shifter housing and the top of the resonator. I had a bottle-type resonator from Vibrant installed in place of the Alta unit to get some more room and things got better. I then had a bit of welding slag from the new resonator touching the black rectangular cross brace, causing some problems, but a grinding wheel took care of that!

I might also recommend checking your exhaust hangers. All of my rubber hangers were shot from heat and stress... a fresh set helped out a lot.