I decided to take off my cat and gut it today. One for better mpg and two for the 2 or 3hp it gives you, which by the way, you CAN feel. Ok got everything hollowed out and put it back on. But when I go past 3k RPM accelerating fast, it makes this weird like vibrating or buzzing sound. It used to always do this if I haven't cranked my car for about an hour or so and then stopped about 1 minute later after it warmed up. It always sounded like it was coming from the cat. But now it does it every time I hit around 2800 to 3000RPM's and then stopped at like 3,100 RPM. Anyone have a clue what this could be? I made sure and got all of the **** out of it including the insulation....

 

There could be a little piece of something vibrating inside the cat, or it could just be the way the exhaust hits the inside of the "gutted" cat causing the exhaust to make a vibrating sound.

The best way is to either buy a "test pipe" or just put a straight piece of pipe in to replace the removed cat.

 

yea that's what Im thinking. Im gonna go with a high flow cat though I think. It's legal and still has better flow. Know any good brands that have cats that just bolt right up rather than being welded and that are under 100 bucks?

 

I saw Magnaflow cats on e-bay for under 100. Depending on your application some were ~ 50.

Vibrations and buzzes are pretty non-descript and hard to diagnose, but is it a rattle like one of your heat sheilds or is maybe the resonance of the extra sound vibating something on your car right there?

How much louder is it? The exhaust I mean.

 

It's not THAT much louder...Plenty noticable but not like way to loud or anything. Im thinking it might be something rattling form something being loose or something I dunno. It's not the heat shields seeing how they are not there anymore lol.

 

i still say the Random Technologies cats are well worth the 200-225 you pay for them. but i know how it is trying to save up for every part.[:@]

 

gutting cat [sm=nono.gif]

 

mine does the same thing and its my short shifter hitting the exhaust, only way it would rattle is if you missed some pieces, and why would you trash a perfectly good cat, you could have sold that to a recycler for like 40 bucks even if it was bad

 

it is not likely...but there is a small chance that when you put the cat back on the exhaust moved...i know when they took mine off and put it back on my cat-back moved and then at certain times my exhaust was rattling against the frame of the car...it was an easy bend-fix...but as i said its probably not going to be that in your situation...p.s. if you think it is that...a place like meineke will pop it up on a lift and take a look at it for you...they put mine up and fixed it for free!!!