What your describing sounds like a utility company problem. I would have them check out their system. Ive dealt with this before on diary farms and pools. It comes from the utility company having an insufficently sized neutral or a break in it somewhere and the ground is taking up the slack. Normally the pocos are resistent to the problem and its not uncommon for them to deny it all together. Talk to them though there is a device made that can be put at their transformer that seperates the customer's neutral from the poco's.
