Thanks for the suggestions guys. I've wonder about the microphonic tube scenario. Based on the video it doesn't seem to be the same issue, but I guess that could vary. I will pull the back off and check to see if any tubes are loose. I won't go much further than that. This amp, although a 2011, probably has less than 50 hours on it and has spent most of it's life here at home. I've had to replace the stand-by bulb and now possible tube issues sure disappoints me.
Sounds like a bone-simple preamp tube problem.
PRS doesn't make tubes or bulbs, they buy them like everyone else, so any issues certainly aren't a result of a fault at PRS. Most amp issues are about the tubes. To complain here that you're disappointed because you have to change a tube on a 2 year old amp isn't a fair criticism.
Tubes - especially modern tubes for a variety of reasons that include the fact that the machines used in manufacturing are growing very old - are a bit unpredictable.
You never know when a tube will go microphonic or fail. You can test a tube one day, and it can measure fine, and then go bad the next time you fire up an amp. I've had brand new tubes go bad on lots of new amps by the best makers.
And you mention that the amp has maybe 50 hours on it - not relevant when it comes to tubes, and some folks feel that the more the old style electronics sit unused, the greater the likelihood that firing them up will blow a tube.
PRS uses European tubes, JJs and Winged Cs, on their US amps. One might have a different preference, but among modern tubes, these tubes have great reputations. They could buy cheaper Chinese tubes, but there would be more problems and they won't sound as good.
When I was a kid in the 50s/60s, every drug store and hardware store had a large "tube tester" that stood on the floor about the size of a juke box. It was NOT an unusual sight. You'd bring in your suspect tubes and test them, and if you needed to replace one, you'd go over to the tube rack next to the machine, and pick up a replacement or two. I remember racks of RCA tubes at the drugstore I used to get sodas at as a kid, with the red and black boxes. If only I could go back in time to get some!
I point this out because changing tubes was a ritual
everyone did on their electronic equipment in the tube era. People didn't hire a technician to change a tube, it was done by everyone.
Every tube amp manufacturer has disclaimers about tubes. Here's what Mesa has to say:
"You may occasionally experience some form of tube noise or microphonics. Certainly no cause for alarm, this quirky behavior comes with the territory and the Tone. Much like changing a light bulb, you don't need a technician to cure these types of minor user serviceable annoyances and in fact, you'll be amazed at how easy it is to cure tube problems...by simply swapping out a pre-amp or power tube!" http://www.mesaboogie.com/US/Dealers/FAQs/faqs.html.
The tubes that come in PRSes have a very good reputation among tube-o-philes, but they are still early 20th century technology, vacuum tubes.
It's probably a microphonic preamp tube, all you have to do is lightly tap each preamp tube with a pencil to find the bad one. Pull it out (you may have to gently rock the tube in its socket to pull it). Plug in a new 12 AX7, you don't have to test the tube or rebias the amp at all with preamp tubes, and voila, you are done. So simple, I did it as a 12 year old on my first amp, nearly 50 years ago.
Really, don't be afraid. If you can change a light bulb, you can change a tube. You don't even have to stand on a ladder to do it (though, hey, if you like standing on ladders, I suppose that's ok, too).
