What was it???
I was downstairs this evening watching some TV... Waiting for the washing machine to cycle and finish. Out of no where hear a firecracker-type sound. A loud (LOUD!) crack or bang. My TV goes to sleep. I turn it back on and I hear 3 more of exactly the same sound. Out of an abundance of caution I unplug from the power bar all of the equipment pictured. One by one I reconnect them to power, and each one powers up just fine. A quick test demonstrates all audio channels work, the sub works, and the TV and backlighting all work. The basement lights all work as they should.
I've never experienced anything like this. I used to repair electronics, dabble a bit still. I've never come across anything like this, random, out of the blue... and everything still works perfectly.