Schmalle

It's true that there is no specialized power amp block. Bummer, right? - Kind of, but probably not really: There are many amps with power amps. Some of the amp models come with a very simple preamp section. You may use that fact to achieve your goal. Try the A30 Fawn Normal or the Tweed Blues Normal. As a rule of thumb start with Bass and Treble to zero and Mids to 10 (if it has a mid control). Why? - Because most amp's tone controls produce a mid cut when everything is set to noon and we want a neutral sound from it. Another approach: Compare the activated amp model (that you use for power amp sim) with the bypassed one. Try to dial it in so that it as neutral as possible to get a feel for the amp and to get a good starting point. Obviously you need to start with the question: What do I want to achieve with this power amp simulation? Saturation? Power amp sag / compression? A different frequency spectrum?

The underlying assumption here is that they modeled the same Deluxe Reverb specimen twice. I highly doubt that and would bet money that these are different Deluxes.

It's a hardware problem of the rotary encoder. Contact cleaner can fix it (at least temporarily). Replacing the encoders can and has been done by members in this forum.

If it is not an external noise source: Maybe the internal power supply started to whine? Could be a bad capacitor or a coil/transformer vibration. Contact support! It would be nice if you report back and tell us the cause for future users.

Well, I read your OP differently. That lowers the probability of it being a no-ground issue. Does your Helix produce this sound without a guitar connected? Or do you have to connect a guitar and open up the guitar's volume for it to occur? - if so - does it change in intensity with the guitar's position in the room? The noise source might be a noise emitting device in the room. So does this occur in a different room?

Ok. Usually this kind of noise can be picked up if there is either no ground connection or more than one (ground loop). We can exclude a ground loop based on your description. The fact that it goes away if the Helix is plugged into a (grounded) amp points to a missing ground connection. Helix is grounded by the power cable which might be defective - so try a different power cable. It could also be an ungrounded power outlet. So try it in a different room.

Which Helix is it? Floor, LT, Stomp?

@mautejIt probably doesn't add latency, because in true spillover mode the DSP's are working one for the current preset and one for the preset that is loading. It's like having two HX Stomps in parallel where only one is providing signal. There is no DSP chaining like in a Path A -> Path B configuration, so I suspect no added latency. I don't have a Helix so I can't verify this with measured data. That said the increase in latency of a two path patch is marginal (a fraction of a millisecond) and shouldn't be an issue.

Setting Global Settings > Footswitches > Stomp Mode to 6 Switch gives you all 6 switches to program in Stomp Mode only (hence the name). Set the Snapshot Command's Press parameter to the snapshot you want to navigate to (instead of Next).

It has to be programed per preset (aka patch). There is no global mode that does what you specified.

Set Global Settings > Footswitches > Stomp Mode to 6 Switch. Use Stomp Mode. Program the three footswitches by assigning each with a Snapshot Command (1, 2, 3) using Command Center. This has to be done per patch.

"Center" is 0%. Tip: Save the block as favorite for easy access and name it "FlipFlopper" or something even funnier. ;) Have fun.

To invert the phase set up a Stereo Width block [Volume/Pan (Stereo)] like this: Width Center, LR Swap Off, Balance R100, Level 0.0dB, RPolarity Invert ...and use a (any) mono block after it. Why do I need a mono block after it you ask? With the above mentioned setting the inverted signal leaves the block on the right channel only (left muted). A mono block after it automatically sums L (no signal) and R (flipped phase signal).

A suggestion would be to use a MIDI monitoring program to track all MIDI messages. Maybe that reveals something suspicious.

A total noob with a cave of forgotten gear? Find the error.