Mark V combo - wooshing sound on Ch1 EDGE mode

Folks,

Wondering if someone can take a stab at an issue I'm having. I got a used mark v combo. Everything works, it just has this very strange swooshing sound when (especially when droning on a muted E string). The settings I'm using are exactly those on the video below except on the Edge mode.

https://www.youtube.com/watch?v=013Geypl49c

I'm still within my thirty days to change the amp for something else but I like this amp...alot..just this issue is annoying as I can't use one mode of my amp. I also notice the wooshing is there on the other channels just not as much. I know its not my guitar as it behaves with other amps.

I spoke with MB customer service, they suggested swapping out Preamp tubes and consulting the manual. The manual points out microphonic noise vs popping noise, I get none of that. I can do the preamp tubes but that costs money and if I end up returning the amp I get stuck with spare tubes I may not use.

Any ideas?

so i bought a preamp tube and tried it in all the tube slots that are tied to channel 2. Still same thing.

Does anyone else get that weird swooshing sound when they dime the treble on EDGE mode? Dimed Treble sounds real good on Crunch channel (more gain) guess not true for Edge mode...

Are you using the 90W mode or 45W mode? If you are using 45W mode try changing the switch on the back of the amp to either Diode or Rectifier.
In 45W mode, the amp is operating in extended Class A so it may be a power related issue. See if the issue is still present in 90W which is a modified Class A/B operation. You may have an issue with the tube rectifier ( even with 90W, if the rectifier tube is not up to par it will momentarily disrupt the DC power of the amp. With the amp set for 90W, the rectifier tube is bypassed by diodes but it is still active in the power circuit and will cause issues if it fails). I would turn the amp around and watch the power tubes as well as rectifier tube. Look for arcing or lightning in the rectifier tube that may occur at random. If you see it, replace the Rectifier tube and the issue should go away. I would not change the tube unless you notice a problem.

I am not very fond of the EDGE mode on the Mark V since I find it thin on the low end and too much ice pick tones in the high end. CH2 is the one channel that can be troublesome to dial in if you are comparing the different voices and using the same preamp settings. V2 preamp tube is the only tube used by CH2 and not used by the other two channels. However you stated you hear this woosh sound in all channels, sounds like it may be related to the reverb turning off and then back on. Try turning the reverb off completely (dial out the reverb as well as turn of the reverb on the footswitch) The reverb circuit shares two tubes with the gain stages of CH3 so it may be difficult to isolate if the issue is related to the reverb.