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I put together a TC15 kit this September, after having built a Tweed earlier this year. The amp is great, and I definitely intend to make a future, separate post to gush all about it. However, the reason I started this topic is that there's an annoying oscillation noise that I can't seem get rid of. Here's a youtube link to a clip I recorded of the noise:

https://www.youtube.com/watch?v=ajaqrqc1qlw

I've tried swapping tubes (both power and preamp) around, as well as plugging into different outlets and testing against other amps to see if the issue was interference, and the oscillation still occurs. The sound it makes is very inconsistent, sometimes coming and going, but it's always at the same level regardless of where I set the volumes of either channel. Conversely, engaging the master volume does reduce the noise along with the audio signal. All this leads me to believe the issue is somewhere around the phase inverter, but if anyone can chime in and tell me what they think the issue is, I'd appreciate it. I don't have an oscilloscope, so if I have to set everything up to do some chopsticking with the wires while the amp is on, I want to be sure I'm looking at the right part of the circuit.

Annoying noises aside, the sound of the amp is incredible, and the custom head and 212 cab were beautifully constructed by Mr. Cohrs. I put a pair of British voiced Webber speakers (the Blue Dog and ceramic Silver Bell) in the cab, and have been thoroughly enjoying using it with my other amps. Once I have the TC15's oscillation sorted out, I look forward to playing it through the cab regularly as well!

Thanks in advance to anyone who can help.

Did you check all your grounding points? These should be solid connections. This happened to me on one build and ground connection was the culprit have fun chasing the faulty connection!

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This is happening albeit in a much weaker way to an amp I built as well. You hear very faint oscillation sounds every once and a while.

Its sound is erratic, sometimes appearing and disappearing, but it remains constant in loudness no matter how I adjust the levels of the two channels. On the flip side, turning down the master level does lower both the audio signal and the background noise.
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This is also occurring to an amplifier I created, albeit much more weakly. Every now and then, you hear very weak oscillation sounds.
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