So I just got my Studio Bass back from the tech and I have to say I LOVE it. It occasionally has some crackling/bacon frying noises that I'm attributing to the fact it was probably drug on the bottom of the Mississippi for about 5 miles, a cleaning of the pots has seemed to remedy that problem. I have been told some of the tone caps are also not quite to spec but that the amp was tested and verified working with new power tubes. The issue is upon shutdown of the amp I get like a pinging sound that's reminiscent of the noise a car's exhaust makes after shutdown as it cools. The tubes are Tung Sol 7581As, and they weren't cheap tubes(as I'm sure you guys know). I've not had the amp at true gig levels yet(because it's simply too damn loud for my house), I will test it on a gig next weekend. I've had a couple of tube amps and none of them ever made this noise so I'm chalking it up to me just not being super familiar with them. Can anyone tell me if this is normal?