Ok first up are their computer CRT monitors or a TV or fluorescent tube lighting near by ? These are all potential sources of noise.

If it is none of the above, it may well be that the guitar has a bad earth.
This is easy to fix. Make sure the bridge is earthed and that all the other electrical connections under the scratch plate are OK.

If the guitar has single coils, which are notorious for picking up noise, there are several things you can do to reduce noise like coating the scratch plate with coper foil etc.

Let up know how you get on.