erd90vettesc

I have a bone stock 90 L98. In the last year it has developed a very annoying metallic buzz or vibration sound from the exhaust just off idle up to about 1800 rpm. One of my friends said it might be catalytic converter going bad. He said when they start to fail junk inside of them will fall to bottom of them and cause rattles and vibrations. My car also has the pre-cats as well. Could they all be failing? At any rate would be best to get the Magna-Flow low restriction front y-pipe and converter to replace this? Thanks in advance for any help you guys could offer.

Co-Vette

Ditto with my 93 LT1.

Also was wondering whether it was coincidence that it started making the noise after it went up on the rack for an oil change - any chance that the rack contacted the converter, or more likely that the thing is just 15 years old and is breaking up inside?

erd90vettesc

Man I have no idea but it is irritating as hell to listen and worse yet it makes my car feel and sound like a POS. If anyone has any enlightening ideas about this please let us know!

Co-Vette

I looked underneath last night, tapped the converters with a small hammer, no rattle. Then I noticed in the back that the driver's side muffler hanger was nice and tight, but the passenger side hanger has about a half inch play up and down. I stuck a large washer between the hanger and the bracket and took it for a ride - noise was gone. I'll order a new hanger for a permanent fix.

I think a bad cat will resonate at a certain RPM, that is what made this odd, it would rattle in 2d when you gave it gas, not anytime at idle (in neutral or in gear).

LvBret

my 87 convertible has a cross brace.. i was getting alot of rattles and vibration under load...

i inspected the cross brace and saw it was touching the exhaust in several places ( i suspect someone either jacked it up improperly or put it on a lift wrong) .

after a few minutes grinding the x brace and creating clearance the vibrations and noise went away..

sometimes the simple answer is correct.

look for things touching the exhaust and you might find the problem!.

Bret

Southern Comfort

Some front exaust pipes are double walled with the inner wall spot welded to the outer wall. If a weld breaks, the inner pipe will vibrate in the outer pipe.

You can tell if you have this type if you can see spot welds between the manifold and the cat.

Happened to me. New pipes solved the problem, but it drove me crazy for months til I figured it out.

good luck.

erd90vettesc

I havent' had a chance to take your guys advice yet, but I will this evening. The exhaust from the Cat back is brand new so and the hangers are new. I know that whatever it is has to be from the Cat forward and the vibration existed before the Cat back was replaced. I jack it up tonight and see what I can find and report back. Thanks for all the insight with this.