Mark IV Issues: Weird lower octave notes & volume swells

[SonVolt]

I recently picked up a Mark IV wide-body combo that's in very good condition and sounds great. I'm having 2 issues with it though.

1) Yesterday I noticed something odd... I have a G Major 2 in the loop that sounds terrific, but with delay there seems to be a weird doubling/octave effect going on at random, like some notes have an additional note ringing out, sounding an octave lower than the picked note. And it's not happening all the time, I just hear it every now and then with playing single note leads. I've used the G Major 2 with my Mark V with no issues, it's not the patch. The issue seems to be less audible as I lower the R3 channel volume. I like to keep it up around 7-8 normally.


2) Every 5 minutes or so I'll get a weird volume spike on Channel 3 that lasts for about 20 seconds and then returns to normal. The tone sounds a little choked when the volume increases.


Any ideas what could be causing these issues?

 

[sduck]

Does it do any of this with the G Major disconnected?

 

[SonVolt]

Does it do any of this with the G Major disconnected?

The volume spikes happen whether the loop is active or not.

As for the weird lower note sound - when the G Major is bypassed it goes away. I'm wondering if there's something wrong with the amps FX loop to be causing this. I don't get this issue with my Mark V.

 

[SixVeeSix]

Clean all of your jacks, your tube sockets and your pots. Test. If it is still happening proceed to the next step.

Replace your output tubes and PI tube. Test.

Will probably go away.

If not then :?: