nasty moan

[FL240SXtoSR20DET]

i just noticed that there is a nasty moan whenever i'm reving my car, or in high rpm. i thought it was my belts, but i tighten them up and i don't think that was the problem. can anyone please help me?<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'>?

[Nismos14]

loose exhaust piping, heat sheild, something in the intake maybe..... could be lots of stuff