My 88 5.0 had an h-pipe with no cats when I bought it. I just put a bassani X-pipe with cats on the other day. I took it out for a drive to see how it sounded, and when I got on it hard, maybe 2 seconds later something happened and the car started to vibrate when i would give it gas. I looked for any part of the exhaust that might be touching the bottom of the car, but there was nothing. I took the x-pipe off and left just the mid-pipes on. When I cranked it back up it was fine, no vibrations, it sounded great. I took the pipes off and reinstalled the old h-pipe and cranked it up and it did the same vibrating crap. The only thing I can think of is that the mufflers are old and something inside broke loose. The common factor in the vibration is that the mufflers are hooked up when it happens. Has anyone else had this problem or think it is the mufflers? Thanks

Is it the stock mufflers that are doing this or are they aftermarket? What kind of vibration is it? Such as do you feel it or is it a sound?

If its a sound then yes the mufflers probably have rust, or a broken piece of metal inside them making the rattling sound.

If its an actual vibration depending on how bad it is it could be normal. Alot of aftermarket mufflers will produce a vibration that can be felt throughout the car.

i know everything in my mach1 vibrates at a certain rpm w/ the flowmasters on...especially when i downshift