I agree that the noise issue alanstevenson is getting is awful, but it is a problem that is baked-in to the the design of the QC, and will never be resolved by any different power supply. The QC can only be grounded by connection to grounded amplification. Without that, the RF interference picked up via the pickups and the player holding the guitar goes right through the chain.
NeuralDSP made a choice in the design of the QC, and there are valid arguments both ways, but we are stuck with it.
The likely reason that Alan’s problem is so bad is that he is close to a strong source of RF interference, and that can come from the most unexpected items. Dimmer switches are well known, and I had dreadful problems with power-line networking used to distribute broadband around my home. Having eliminated that, I found that the transformer powering an electric reclining chair was also a culprit. I suggest that Alan experiment by moving to other locations, and by unplugging other electrical items.
Don’t overlook anything - fridges and freezers, TVs etc on stand-by, computers - I even unplugged my pond pump to check. The power line networking produces a ripple on the mains, and even made valve amps unusable. It’s nothing new - people as old as me might remember getting AM radio through their guitar amps!
LED lighting is also a source of RF, especially some overhead lighting has caused me issues in the past.
Are the fish still alive?
YIKES, lets hope! 
Interesting (and, I’m sure, frustrating) that you guys are having this ground-related issue. I’ve been using mine in the studio, at practice and just played my fifth gig with it. I did a fair amount of my initial programming, switching between monitors and headphones (with nothing eles connected) and the QC has been hum-free everywhere.
The fish are fine thank you. I only switched off each item for long enough to check if the hum disappeared. The main problem was power-line networking, but who would have suspected an electric reclining chair? There is still something in my home (or nearby) causing interference, but I have never identified it. It doesn’t cause a problem with the QC or any of my current gear, but I had to return a PRS valve amp because the noise was ridiculous. With RF interference you do have to check everything.
I’m wondering if we attach a ferrite ring core to the power supply if that would help with the RF Noise. Hopefully someone with knowledge of these could chime in. My situation with the noise is apparent when the unit is powered off while connected to powered speakers. As soon as I turn it off, I can hear a radio station!
In the VERY early days just after release, someone claimed the rings helped, but then as other users started trying them it definitely didn’t work for most of them. Can only report that you’d probably have to try it yourself and see if it helps in your situation.
If you are connected via XLR to powered speakers that use a properly grounded power supply, you should have no grounding issues. RF interference should be much reduced. If you are picking up radio it implies that your guitar strings and electronics or cable are not shielded. My first check would be to ensure that your strings are connected via the bridge, through a ground wire, to the outer shielding connection of your jack socket, and that your cable is good quality and properly screened. It would also be worth checking that the wiring to the jack socket has not been reversed.
I am experiencing similar noise issues, either RF or ground-related, in multiple locations, output through various gear, etc. I have troubleshooted everything recommended, aside from unplugging every item in my house, which I cannot do because I rent an upstairs apartment. I have already been given a replacement QC as my description of the issue led Sweetwater and Neural to deem it defective, but in the end it was not.
I’m probably going to try out the Globtek power supply - but you’re saying there’s no way this would resolve the RF issue?
I brought my QC to a friend’s house and used the same inputs (guitar, cable), and the same outputs (TRS to mixer to PA). The QC had extra RF or ground noise and his HX stomp (powered by a OneSpot) was clean as a whistle. How could this issue be anything other than the QC or its power supply?
Sweetwater and Neural are giving me absolutely no help here, so any input is appreciated.
boot the QC fully before you plug in stuff into it. let it get to the main screen before you start plugging in cables in the back. it does checks on bootup and sets some stuff based on scans during bootup time that are affected by having stuff plugged into the jacks in the back.
i never have this problem anymore because I do this, wherever i go.
Hey equivocal, that’s got to be really frustrating. So, when you say that Sweetwater decided that your first QC was not defective, do you mean that it was quiet when they tested it? Do you have the noise when using factory presets? How about when using headphones, with and without other grounded gear connected? I haven’t noticed a difference but some folks say that it’s quieter with the master volume cranked. I leave all of my external devices connected but it would would be worth trying DeadCircus’ suggestion.
I had tried all of these suggestions with the first QC… I haven’t with the new one but assumed it would be the same since the issue was once again occurring right out of the box. I don’t know how Sweetwater tested the first QC, but they confirmed on their end it was not defective. Noise is present with all different types of connections (using headphones, connected to studio monitors, PA, via USB to Macbook), on factory presets and user created presets.
I have ordered the Globtek power supply people have recommended. It’s the only other variable I can reasonably assume would help the situation, despite what @NigelGBR is saying. Otherwise I may just be SOL with the QC for now given my current location and living circumstances, as I can’t really troubleshoot disabling breakers and unplugging appliances from other people’s apartments. Only other possibility could be a lack of properly shielded cables, I suppose, but I know many people have not had issues with their standard instrument and XLR cables.
I’m really hoping the Globtek makes a difference because I’m excited about the QC, but it has caused me a pretty large amount of impedance to my creative setup and anguish trying to get this issue sorted. Seems like for the price and everything that’s gone into it, the QC should have less problems than a pedal like the HX stomp which is 1/3 the price.
Swapping our mic/line and guitar cables is always important, when troubleshooting. I’ve had cables that worked fine with all but one piece of equipment. Electrons can have a mind of their own. Also, have you tried it with another guitar? If you turn down your guitar’s volume or unplug your guitar cable from the QC, does the noise go away? I apologize if you’ve mentioned any of these things in a previous post.