My wife'* 2000 Bonneville started making a loud rattling noise at startup and when accelerating. I let it cool off and got underneath the car, couldn't find anything loose. Cranked it up and it appears to be coming from the exhaust system, sort of a "tinny" sounding rattle. Doesn't do it when coasting or idling, only when accelerating. Car has about 95k miles on it.

does the car also seem to have a loss in power at higher RPMs?

Possibly the resonator.

There doesn't appear to be any affect on performance. Excuse my ignorance but what exactly is a resonator?

It is the big long muffler like tube in the middle of your exhaust after the cat. It is used to keep resonant harmonics in check and keep the exhaust quiet.

I used to work in a Muffler shop. There is a comb like biscuit inside the catalytic converter, and if it breaks up, it will rattle. Take it into a Muffler repair shop, they will be able to tell you.

Well it'* definitely the cat. Does anyone know where I can get a deal on a replacement? What is the part number? Thanks.

You should actually be able to pick up a high-flow unit for much cheaper than an OE replacement would cost.

The Magnaflow/Carsound unit that fits your car can be had for 50-60 bucks as I recall. The exact part # escapes me, but if you do some searching in the Performance section for high-flow cats, you should find it. Or start a threar about it.

There are other cat options as well, Im running one completely different than everyone else here, but only because the Magnaflow I bought wouldnt fit, I also have a different exhaust setup under there than you do.

But I wouldnt get an OE replacement, its too expensive.