Nanci,
Let me echo Tsolanto's reply. I have indeed had to find and repair this very problem several times in my career, and it is always (in the ones I've fixed) a problem with grounding and current taking the incorrect path.
Check the service first, something could be wrong with the service neutral, the grounding electrode conductor, or the main bonding jumper, those are the first biggest offenders.
Then you have to start with how all is bonded, do you have ground wires serving as neutrals ANYWHERE in the house? If so, that's a problem and a potential source.
Take a meter, the problem lies between the DWV (Drain, Waste, Vent) and your handle, put one lead on the drain, and one on the handle. You should get a voltage (it may be low, wet soapy people conduct minor voltages VERY well), now turn off things in the breaker box until it goes away. If it never does, it's a utility problem........most likely.
You realize this is a difficult thing to diagnose? I'm only providing some of the paths, and the most probable.
I really hope your electrician did not phrase it like that, if he did, that scares the hell out of me.
Let us know how it comes out.
