In a previous post I mentioned ground lifters as a solution for noise issues. I also mentioned that using them can be dangerous and in fact illegal but that it was a topic for another post. This is that post.
Everyone is familiar with the lowly ground lifter. Cheap molded plastic with a place for a three prong electrical plug on one side, and just two slim blades on the other. They're cheap, easy to carry in your go box, and they can sometimes eliminate buzz in an audio system. But if used incorrectly they can do anything from give a guitar player a nasty jolt of phantom power to the lips if they get too close to a mic, right on up to electrocution.
The intended purpose of those little buggers is to allow you to plug a new appliance into an old outlet WHILE STILL GROUNDING IT PROPERLY! There's no lifting intended here. All of those "lifters" actually have a little tab or a short piece of wire with a spade lug on the end to allow you to connect it to the screw on the front of an outlet. If the building is wired correctly, even if it predates three prong outlets, connecting the "lifter" to this screw provides a connection to earth ground for the third pin on your device.
Using said devices to lift the ground is illegal. There's just no question about that. The ground is there to provide a low impedance path to earth for stray current. If there is no path for stray current it could easily find its way into your guitar player and kill them. The first person they'll be looking for to pin liability on will be the ignorant fool the plugged in a ground lift. Yes, if you use ground lifters I'm calling you ignorant and a fool. I will also physically fight you if you meet me in person and try to take issue with me on this. I was an electrician in a hospital and I'm way more up on the dangers of bad grounding than you are. And also I like smacking fools.
That said Brethren of the Knob and Fader, if you've got Buzz Lightyear for a guest soloist on your system, try direct boxes. The ground lifts on those are legal and often have a positive effect. If the problem persists, learn how to trouble shoot and dig deeper. If time doesn't allow, fix your gain structure to make the best of it and get on with things. DO NOT be responsible for harm to another human being because you chose to misuse electrical devices.