While indeed the earth is a very massive object capable of producing a lot of gravity, we should all realize that every object of any size exhibits gravitational pull, and as such, should not be discounted. I've found that the gravitational fields produced by my CRT monitors effect the way the electrons flow in my stratocaster pickups. The gravity from my 20lb monitor seems to be enough to pull the moving electrons from their normal laminar flow streams, thereby creating turbulence. The result is that they bump into each other more, creating a lot of noise, which seems to manifest itself mostly at multiples of 60hz.
Unfortunately, the centripetal forces acting on the electrons rotating around the bobbins are usually not enough to overcome the induced turbulence. However, I do find that turning to the left away from the monitor while playing will sometimes puts me over the threshold by adding just that little extra centripetal force. Note: Our Aussies and South African members should turn to the right, due to the Coriolis effect. They may also wish to rewind their pickups in the reverse direction to the US standard (with 99.9999% OFC of course).