http://freesound.iua.upf.edu/index.php
Has all kinds of sound effects, ambient noise, synthesized music, etc. You'd just have to search for it, and as far as looping goes, you may need to find a decent sound editor to do that (reccomend CoolEdit Pro - bought out by Adobe and now they call it something else). If you do use anything from this site, be sure to credit the creator (per licensing agreement for royalty-free sounds)