When we play our electric guitar through an amp, we are being bombarded with sound. Not just the amazing, lovely guitar tone we all love so much but if we’re not careful, also with a huge dose of noise too. Noise can be hum, hiss, buzz or just white noise. There are several causes for a noisy guitar and I wish to highlight a few of them in the hopes to clarify what’s really going on. The noise that’s known to most people is the noise of the 50 or 60hz cycle of the power that comes out of the power outlet. That hum can be cancelled out at the source of the electric signal via a humbucking pickup. What you’re essentially doing is canceling out that frequency, and because it’s no longer there, it can’t be amplified by the amplifier even though it’s the amplifier that has the 50/60hz hum… The other source of a noise guitar is the player. We all know what happens when we touch a guitar: the hum and hiss that’s present in the sound goes away. That’s why strings with a coating need to have a conductive coating, and that’s also why the bridge has to be connected to the ground of the guitar. But why does that hum go away when we humans touch the strings? For that we have to go to the source. The air around us is filled with electromagnetic waves, otherwise known as radiation. The majority of radiation is absolutely harmless and much of it is generated by humans: for example radio, television, wireless internet for your phone or tablet etc etc. The device that’s intended for that radiation has an antenna that picks up the signal (which is, essentially, a controlled form of a specific type of radiation) and in response, that antenna sends a signal back to be picked up by another antenna. That’s basically how your phone or television works.
We humans are made up of 70% water with salts, and a saline solution is quite a good conductor (that’s why you should never, ever work with electricity near water!). Because we’re so incredibly conductive, our body acts as a huge antenna! We ‘pick up’ the random signals around us and send a similar signal back. That signal is a wave of an electromagnetic nature and since our guitar pickups are also of an electromagnetic nature, they pick up that strange, random noise. Since the electromagnetic wave our body produces isn’t a constant, even the revered humbucker can’t cancel it out. In fact, it picks it up even more strongly. But because we are an antenna, we can ‘short out’ the antenna by hooking it up to the ground of the system that amplifies the signal the antenna produces. And that’s exactly what happens when we touch the strings. The strings are connected to the bridge, we touch the strings and bridge and wham: grounded. No more antenna. No more ‘white noise’ to be picked up by the pickups! Sometimes you also hear a little buzz or ‘pop’ when you touch the strings. That’s perfectly fine and absolutely not harmful. That’s the static electricity of your body jumping off to the ground. Static electricity is what you get when you run your hands through your hair, for example, or when you rub ferociously on a woollen sweater. That charge has to go away somehow. It can degrade over time, but if it finds an easier way to go away (for example a piece of metal connected to a ground), it will surely do that.

Some people take ‘grounding a guitar’ a bit too literal I’m afraid.

I hope I clarified a bit how your guitar works and how you work in relation to white noise. There are, of course, other noises and buzzes and hisses but most of them are related to the ground. The ground wire of the bridge may be connected badly (in other words: you, the antenna, isn’t grounded properly!) or the pots aren’t grounded properly.

I know that it sounds a bit scary – shorting yourself out – but it’s absolutely fine and not harmful in any way. Remember that ‘creating a short’ means nothing but ‘closing the electrical loop.’ An electrical loop that’s open ended can be more dangerous than simply closing the loop!