Elz, these comments are worth every penny you paid for ‘em.
Given that the noise could indicate a serious problem, if it is a molded-case breaker, get the client rep to let you remove the breaker front cover while in service, {it should be removable if having an interchangeable trip} making every reasonable effort not to open the breaker, but very plainly understood that you not be liable if it happens.
If it is a so-called “critical” load, would the client prefer to prepare for a trip while you are there, or at another time when you might be an hour away and him desperately needing to find a fried-breaker replacement—should that be the only damage during unscheduled failure?
I get the “Where’s your dual-redundant everything?” stance when people start demanding immediate and absolute answers, sometimes followed by a “Please show me your scripted contingency plans for loss of power to this system.” and, “You mean to tell me that a single-point failure will cause some sort of operational disruption? Who decided on that brilliant scheme?” [There are financial operations and data centers that spend serious money on equipment and planning—having learned from expensive mistakes.]
If the client won’t buy into your plan, walk away and don’t lose any sleep over it.
Thermal imaging or AC millivolt-drop tests could be made with the breaker in service. Noise may be from high harmonic current in the circuit.
It may be apparent that over the last decades, I have become cynical and impatient with clueless, self-important, dime-a-dozen hotshot, junior-MBA managers that demand supreme, unfaltering NASA-grade reliability from electrical gear that they barely paid Wallmart prices for, particularly under the guise of protecting their precious data of value akin to the Dead Sea scrolls.
[This message has been edited by Bjarney (edited 08-17-2004).]
