When I turn on the engine from the inside of the car, it's so quiet so I never though of opening the hood.

Today, as I was accelerating hard, I heard different noise. It's wasn't the engine roaring, it was more like an air sound?

Anyway, I then proceeded to open up the engine and listen to as it running.

When I opened the engine, it was much louder then I though. The hood really insulated alot of noise.

It sounds kind of like a knocking noise on idle... You can't hear it when the hood is on, but when the hood is off it is really loud. Can someone verify their engine sounds like this also?

Should I take it to Acura or is it just normal?