1990 Olds delta 88

I have a 1990 olds 88 that had the cat. converter replaced, but for some reason on occasion the car gets loud like the exhaust has a hole in it but then goes away. If it was exhaust related wouldnt it always sound loud?? It gets louder when I accelerate. Any possible solution or advise would be appreciated. I have taken it back to the muffler shop but they don;t find anything wrong with it?

Is it getting loud as in exhaust loud, or is your motor just revving up high?

If it is over-revving, then your ICM may be going bad.

I dont know on the loud exhaust part though...if the exhast system checks out fine, then the muffler people are probably right....but have you taken it to more than one shop? A different pair of eyes may see something different.

Also, is the new muffler high-flow or to stock specs? If it is high flow then I would think that you would naturally get a louder-sounding exhaust....

It is a wierd problem...this is the best i can think of. Anyone else?