The sound of electrolytic capacitors failing

My system (all 20-30 year old high end gear) has started to have a sound problem. I'm hearing some breakup on peaks and a few Db shift to the right side in balance for the first hour or two of playing. At some point after that, everything suddenly snaps into a proper sound, usually in the middle of a song. I know the problem is either in my preamp or amp. Could it be one of the power supply caps breaking down? Any other ideas?