I have a 1994 z28 and recently put the magnaflow cat back on. I have had tremendous issue with the over axle pipe. It touches a cross member down there and at 2500 rpms makes a horrible rattle and vibration. Has anyone else had this problem or any solutions? We moved the whole pipe up and re-tightened all the clamps and it was good for about 2 days and then started touching again.

 

The intermediate pipe goes over the upper panhard rod brace. I'm assuming that is what you refer to as the "crossmember". The rattling would likely be caused by excessive up-and-down movement of the intermediate pipe. That is controlled primarily by the rubber block in the hanger on the passenger side muffler inlet pipe. Is that hanger in good shape? The similar rubber in the hanger on the driver side muffler outlet pipe could contribute to the problem. If that's not where the problem originates, start looking at the hanger in the front by the cat..

 

That is what I'm referring to as the crossmember. Also yes the rubber inside of the hanger on the passenger's side has some considerable wear to it.

 

I haven’t seen any significant number of complaints over the years about the Magnaflow system. Seems to be good quality.

 

I had this same issue with the same catback. The problem was I did not have the pipe inserted far enough into each other. I used a rubber mallet and that did the trick. Good luck.