Strange buzz in my guitar

I'm hoping someone will be able to help me figure what my problem could be.

I have an '84 Peavey Horizon II guitar. Here's the pic of it at the end of the post...

It seems to have developed an intermittent problem. Sometimes it makes a hum type of noise, kind of like a gound lift switch needs to be turned on or something. It's worse when I have any of the pickups configured in a single coil mode. The noise lessens when I have the neck and/or bridge pickups in a humbucking mode and have the middle single coil turned off.

Now, here's the strange part ... lay the guitar flat on its back ... and the noise goes away completely. Return the guitar to a vertical (playing) position and the noise is there. AND ... this noise pops up for 1 to 3 days at a time, and then goes away and doesn't come back for 2 or 3 or 4 weeks.

My guitar fix it place can't makes heads or tails of it. It's definitely a problem inside my guitar though. Anybody ever heard of this??? It doesn't happen very frequently, but when it does, it drives me nuts.

Any comments or help would be greatly appreciated. Thanks.

It sounds to me, just like you said, it could be a ground problem. This can be caused by a loose/bad connection in the grounding. Since your guitar is fairly old this is a good possibility. Also contributing to the sound could be bad shielding. Older guitars had poor shielding becuase manufacturers didn't know the importance of it. The only way to be sure is if you open her up. The noise that you experience when you have the humbuckers tapped in single coil mode is going to happen no matter what. Unless you wire it to activate the whole humbucker but only transmit the sound from the coil that you want. That can be done with a kill switch wired to the coils you would "knock out". But since your priority is to figure out why your guitar makes this annoying noise, I suggest taking it to a shop unless you feel comfortable using a multimeter (voltmeter) and working with a soldering iron. If you do feel comfortable you can simply open up the guitar and check all the connections throughout the guitar. Check for fluctuation in the read out. Also it might be a good idea to wait until the guitar acts up again to take it apart. That way, if it is a loose/bad connection, you should be able to spot a little easier. Hope you get it figured out. Good luck!

[font=trebuchet ms]It's always good to make sure your guitar is less likely to receive noise, but it also helps to reduce the number or strength of any noise sources. Are you playing near any noise sources like a computer monitor, TV set, air conditioner, or fluorescent lights? You may be able to find the source by walking around with your axe plugged in, and turning in different directions. You may also find that using a different AC power outlet for your gear cleans it up a bit.[/font]

Thanks for the replies! :) This is a great forum!

I'll go over it again when it's being strange.

Yep, single coils are notorius for the hum. That's how humbuckers got their name, 2 single coils put together cancel's the hum, hence the name humbucker. I'm agreeing with most of the others, sounds like a ground wire might be loose.

I didn't know that about the humbucker name. Thanks!

Well, the poor ole axe is sounding quiet and clean today. But when it messes up again, I'll be all over it with my trusty volt meter! ;)