I'm still trying to understand, so play along with me
I have to assume since you say it sounds like a go-kart, it's an engine-related sound. I seriously doubt this is your timing belt cover causing this. My belt slapped the cover for a while - I took it off - but the sound it made was negligable(sp?) to anyone but myself.
Sound like it's coming from an area forward of the firewall? Can you "home in" on it with the hood up and the engine running? Maybe you have a leaking exhaust (catalytic converter, cracked/loose exhaust manifold, etc.).
I didn't check to see if you list any mods, but if you're running an aftermarket intake, the filter may be loosely mounted or damaged.
Also, timing itself can cause differences in engine tone. I have an exhaust cam out of time right now, and I can hear a difference in the engine for sure.
Aside from noise, any other side effects? Loss of power, stumbling, etc.?