I had a new cat-back exhaust put on my 91 Formula 350 by the good folks at Meineke about 2 months ago. I would have rather done it myself but I don't have a garage. It's a custom bent 2.5" exhaust with a Flowmaster 80 series muffler. Three times now I've taken it back in for them to "adjust" the hangers so that the infernal rattling will stop. It's fine for awhile but then after a week it starts to rattle again. Now the system only rattles only around 1400 RPM and only when in gear. I could just look at where it's rattling if it wasn't for the moving at 45mph thing. The noise is definately coming from the rear somewhere. Now to my actual question, the head mechanic at Meineke said that the 2.5" pipe is just too tight of a fit over the axle. That doesn't make any sense since some people here are running 3" systems. I think they are just using crappy hangers or he bent the pipe funny. I would like to know if this is a known issue upgrading from the factory system and how can I fix it. Thanks.

i wanna know why you choose 2.5" instead of 3".. 2.5" is too restrictive in mu opinion for a 350..

but to help ya out. the thing about 2.5" being too much to easily fit over the axle is total .. your right, 3" pipe fits over perfectly.. the rattling might be coming from the muffler itself, iv seen a common thing with flowmaster 80 series to hit up against the rear heat shield, because they have to be angled up at one end. So it might be rattling there. if they were smart they would use rubber isolated exhast hangers so that wouldn't be the problem.. Check to see what kind of clearence you have around ur muffler

I chose 2.5 because the stock cat is 2.5 and I will not be ready to replace my cats until I get headers.

They did use rubber isolated hangers actually. I don't think it is the muffler itself rattling againts the heat-shield, there should be enough space. I'll check for sure in the morning.

That might and might not explain it though. Since it takes about a week after they adjust the hangers, it's logical to assume they are settling somehow or the rubber is stretching. But if the rubber is stretching then the muffler should get farther and farther away from the heat shield. Unless of course they had it pressed tight against it in the first place but I don't think so. I suppose the rubber may becomig tighter from the heat.

I guess I will just have to poke around under there shaking it somemore and hopefully I can find it.

Thanks.

Mine hits the heat shield and I can only hear it around 1500 RPM while driving. I loosened the sheet metal screws and bent it up a little, but it still hits on the right side. I might try some spacers behind the brackets on the frame, but it's not that big of an issue for me right now.

My muffler rattles too, I clamped the inlet to the stock I pipe and it was too short of a run, so my left tailpipe always rubs up against the well in the back. Its a real pain cuz whenever i pick up girls after school i have to turn the radio up to drown out the darn rattling back there. I'd start the car and look under it to see what u can do with a ratchet, I know u can't look under it at 45 mph but see what u can do by yourself, I put mine on, so I know what is up and what is not. Lemme know if I can help you out more, cya dude.