well,
the first thing to do is determine what the source of the noise is. I know this is probably a no brainer. Is the noise coming from your guitar amp? mic pre? sound card? flourescent (spelling?) light? bad grounding of your power?
do your best to isolate the noise, then you can start figuring out how to get rid of it. a little more info as to what you are recording and through what equipment may help others who are reading help out.
-j