I was out of town last week, doing a cursory "PM" on a small service for a computer center, and noticed that one breaker's trip unit was making a barely audible sizzling/snapping sound. The current draw was only 20%, and there was no evidence of loose connections or discoloration. Since this breaker fed some vital UPS equipment and another computer equipment panelboard, I didn't want to even THINK about shutting it down to replace the trip unit. BUT, it would be good to know if some noise coming out of a trip unit is at all normal. Anyone have experience with Westinghouse breakers' trip units (in a Cutler Hammer switchboard)making noise?