one thing... before you crank 'er down tight again, blast the connection with some air incase any crud has gotten down in-between the header and the head. That way nothing gets pinched in the gasket.
Can you tell if it is a squeeling belt or is it a bearing somewhere? If belt dressing does not cure the squeel it may need a turn or two on the adjuster.
If you choose "search" above and type in just "tighten belt" you will see a bunch of different threads about how to adjust 'em, finding where the noise is coming from, etc... Depending on what you were wheeling in though, it may just need a good cleaning.