[Chris_B]

Everything is sorted out with the Microzotl preamp.  I finally contacted Mark at LTA and he was aware of the issue and quickly fixed it.  Apparently, there is a noise pickup issue associated with the volume board that is audible with sensitive speakers and/or high power amps.  I just happened to have both. The fix involved rerouting some wiring and changing out a couple parts.  They had the preamp back to me in 24 hours and it is dead quiet now  .

[bluemeanies]

I had a similar problem when I installed new Shaguang CV181"s in my SP14. I had a slight whooshing sound coming from my midrange.
What I did was simply switch the Output tubes to different locations on your pre-amp.
It worked!
Speakers are dead silent.
Hope this helps.