system hanging for 1-3 min

I've notcied a weird problem on both my SUSE 9 and sle8 systems. It hangs, for periods of 30sec-5min, then starts working like nothing has happened. There is nothing in the logs to give me any clue, and everything always seems to work when it comes back. Currently Im using version 9 with dual AMD's and about 8GB of ram. Has anybody else seen or been able to resolve this problem? Thanks, Keith