If I put my Triaxis on Lead One Red, it makes a high pitched squealing noise. Is this a microphonic tube?
If so, I've read a lot of people saying swapping out the original Mesa tubes improves it, so maybe I could do that if one needs replacing. Is this easy enough for a non-techie (why doesn't this word end with a Y?) to do?
Could be a microphonic tube. Changing them is super easy. Just pull it straight out, and when you put a new one in, make sure to align the pins correctly.
There's a thread started by Vince about TriAxis presets and tubes. Check that thread, it'll tell you which tube is for the Lead 1 Red mode.