I was bored and pulled some gear out to mess around the other day. Connected a monitor that I had modified and tested a few months back, powered up a rack with a MR18, no input device (music or mic) connected at this point, then I turned on a QSC GXD8 amp, the speaker let out a bellowing sound that dissipated quickly. I thought crap it probably got my HF driver, but it didn’t.
What could it have been? It sounded like a build up of energy, like capacitance. Is the issue with the amp? I have only used these GXD8 amps a couple times. I periodically would get a failure message from one, carried it to a service center and they said they could not get it to recreate the failure.
A few years ago I had a similar event at the venue, QRX 115s and Crown XLi amp, but this was a the end of the night and it happened a couple times, muted mixer, walk up to rack to power down, when I powered off the amp I would get this HF kind of bellow that dissipated quickly from the QRXs. This amp did eventually fail.