I have a two hum bucker guitar with (amongst other things) a coil split switch mounted on a push pull. I haven't had any issues with hum before but suddenly today for some reason I have started getting quite a loud, clear humming sound with an almost crackly sort of quality to it, when I am in single coil mode playing with gain.
I've tried changing all my cables and playing with the EQ on my amp, and also checked all the ground leads in my guitar, including the leads which ground the guitar through the bridge. My guitar is fully shielded by copper lining on top of shielding paint. Nothing seems to be any different to usual, all connections are fine and in humbucker mode there is no noise at all so I don't think it's interference. One thing I have noticed is that unlike it has been before, touching the stings to ground the guitar makes no audible difference to the hum. That's kind of how the hum sounds - like a single coil guitar when you don't touch the strings, and it doesn't get any quieter when I do touch the strings.
I know this is a common problem for people with single coil guitars but it hasn't been anywhere near this bad in my guitar - the hum is now just about as loud as the actual signal! Unfortunately I'm at uni and my other guitars are at home so I can't try another guitar to gauge where the problem is.
I use a dead simple rig:
Guitar --> '91 Mesa Boogie Mark IV --> (effects loop) Lexicon MX400, Ernie Ball Volume Pedal --> Back into my amp
If anyone has any suggestions I could try I'd be really grateful!
Troubleshooting noise problems over the internet is devilishly difficult, this is an area where "hands on" means a lot.
And you've done most of the simple things already.
As you've already surmised, the two main possibilities are a change in the electrical environment, or something haywire in your guitar.
As for the first, if changing cables, etc. made no difference, let's try to rule out an environmental change entirely. This means taking your guitar and amp somewhere else to plug in- in a different room, but it also must be on a different electrical circuit.
If the hum is still there, we can then effectively rule out causes external to the guitar.
One thing I have noticed is that unlike it has been before, touching the stings to ground the guitar makes no audible difference to the hum.
This suggests that the hum is is unrelated to a bridge grounding issue. And while single coils can be noisy, if the hum is as loud as the signal, coupled with the fact that it's a sudden change in this guitar, that's not ordinary SC hum.
This all suggests that attention should be focused on that push/pull switch. The possibilities there are threefold: Bad connection to the switch, connection is touching something else (shielding, other components, etc.), or internal switch failure.
The above list is a rough "order of probability" as well.
Now, several questions. First, since you're at school, do you have access to a soldering iron, tools, etc.?
And the biggie: Does this switch cut both HBs to single-coil simultaneously, or just one of the two?
If the answer to the second question is "yes", please also check to see that you are in fact getting both SCs when the switch is pulled. Use a screwdriver or other metallic object to tap each coil. With HBs, you have to be careful, as tapping a non-operative coil will still induce some signal in an operative coil, so the difference can sometimes be a bit subtle.
But if you are now getting only one coil, that might explain the noise. Usually, if the switch is set up to cut both pickups to SC mode, the coils are set to be hum-cancelling (one N coil is coupled with the other pup's S coil). If you're only getting one coil now, that could explain the increase in noise.
that's all really useful thanks. I have had another poke around but nothing made any difference. It is a master coil split so one switch does both pickups, and yes I did bring a soldering iron with me (a necessity for anyone who has built their own guitar!). Bizarrely though it seems to have sorted itself out now after I changed the pickup rings for some nice shiny chrome ones. I have made a sort of quick release pickup system in my guitar and when I disconnected the pickups to change the rings I noticed a dodgy ground wire which I fixed and anyway after I put it all back together I had no issues. So no worries any more but I'm still mystified as to what caused it because the hum was on both pickups and only one pickup wire was frayed so who knows!
Thanks for the info again it gives me stuff to try if it goes wrong again, and I'll definitely stick with this forum you guys seem pretty clued up.