Audio Research VS115 - click, snap -did it arc or not?

After many years of just enjoying reading all the knowledgeable posts here I now have a question on how to deal further with this amp. 
What happened? Set it up through the balanced inputs (removing the bridges) and connected Audiostatic ES300 speakers on the 4 ohm tap. Source is a dbx venu360 delivering everything above 100 Hz to the VS115, everything below to the subwoofer/amp. It plays nicely along until suddenly there is a pronounced click or snap, having read about resistors being taken out when tubes go bad on ARC equipment I immediately darted off and yanked the power cord from the outlet. There was no smoke or bad smell, but I let it sit for a couple hours and then proceeded to take of the plate and found nothing burnt on a visual inspect. Next was a simple check of each tube for filament and shorts (checking each possible connection with a mulitmeter it should only return low resistance for 2 and 7 for the KT120 and 4 and 5 for the 6H30). All turned out fine. So now I am wondering what really happened and how to proceed, out of my location sending it to the manufacturer or finding a technician is not my first choice.
Assumption A is that all I heard was the relay (which comes on 5 secs after power on, I couldn't find a reference to it in the manual but would assume it is a plop protection for the speakers) and have to wonder under what conditions it would come off (undervoltage or exceeding current to the speakers)?
Assumption B is that something "went" and needs to be found out. Would you take out the tubes and go part by part and compare value vs. measurement on resistors, caps etc. I do know that in a network values will interact, but a failed component may come up, drawback is the amount of time involved. Alternatively power it up connected but with no signal and measure each bias output (on the back)...all the while ready to yank the power cord immediately.

Cheers
Brxl