In a thread someplace here a few days back, someone mentioned that his
VFD wipes out reception any line powered AM radios in the house. I had
this problem too. I installed one of these:

http://www.halted.com/commerce/catal...=1137198604625

or same page he

http://tinyurl.com/dxlc5

I installed one each on the incomming power line on both my VFD driven
mill and lathe, right in the VFD cabinet, and PRESTO! the noise is gone.
Even a radio in the shop a few feet from the VFD is fine. VFD's are
notorious for sending switching hash down the power lines. These handy,
cheap little filters knock most of it out. It is important to ground the
case of the filter well. In my case, the regular power line ground was
plenty. I also have my VFD's mounted in metal cabinets, also well
grounded, just for good measure, which generally helps.

This is installed on the incomming power line BEFORE the VFD!

Make sure that the filter you get has adequate voltage/current rating
for your application, of course. HSC (www.halted.com) has a bunch of
others like this in various ratings. As HSC is a surplus place, these
are pretty cheap. No connection with HSC, blah, blah, blah, it is just
where I bought mine. Lots of other places sell them, though I think that
full "catalog" price would be significantly higher. I have not really
looked though. Google "EMI line filter" and peruse tons of hits.

There are 3 phase versions as well, not sure if HSC lists any.

Thought someone may find that helpful.

-AL A.