Sabai, I did try a Topaz unit and also tried the Exact Power unit recommended by Nagarch. I actually preferred the Exact Power. The isolation transformer actually was prone to mechanical noise. At the time I was living in a triplex in CA and the power fluctuated quite a bit from 110V to 118V. When my neighbor used her hair drier or turned on her AC unit the effects the transformer made lots of noise. Probably something getting injected back into the power line causing it.
These days I use products from Alan Maher Designs. I have been quite happy with them.