I know exactly the sound shes talking about. If it wasn't for her other thread with the P300 code, Id be stumped.
When I bought my car, it had a P300 code. When you would accelerate, (my car wouldn't go over 20mph) it made a growling type sound in the engine bay, and yes a school bus sound would be an accurate name for the sound. Turns out my cat was plugged.
And since you said you have a little bit loss in power, Id go to a shop (not the dealer) and have them back pressure your exhaust. Id be willing to bet you have a partially clogged cat. Like I said mine was so bad the car wouldnt go faster than 20mph. So get that checked out. And if its not a plugged cat, id be stumped.
Hope this helps.
