Martin, If I were a gambling man I would bet on somebody using either an Ethernet over powerline or some other kind of multiplexer that use the AC wiring to distribute a signal or make a connection that is inconvenient to do via actual installed cable. Does the signal come and go at different times of the day? Is it a steady signal or does it modulate? All the best, -mark On Tue, Aug 30, 2011 at 2:07 PM, Martin Fisher <[log in to unmask]>wrote: > Hi gang, > > FYI, the following is cross posted to two list serves. > > A mysterious squeal appeared in the transfer chain here in the audio lab > about two months ago. It's a tone centered around 10,330 hz and seems to be > coming in on the AC power lines for a good portion of the building. This > has been determined by taking a piece of equipment (in this case a > Soundesign 8 track deck with integrated amplifier and a pair of headphones) > and plugging into several outlets in the building. The tech power outlets > for the recording studios are clean as well as some outlets on the 2nd floor > but many of the 1st floor outlets have the offending tone present. > > I've tried isolation transformers and low cost IsoBar type line > conditioners with absolutely no luck. The tone appeared at approximately > the same time of a revamping of the air conditioning system for the building > and stringing of lines for some sort of digital cable. One of the campus > electricians did some switching around of breakers and various things but > nothing has helped. Before I go out and get a high end line conditioner to > try out I thought I'd tap the collective wisdom of two of the best informed > list serves. Any ideas?? I'm sure I've not provided the best description > in the world so I'll try to answer any questions that arise. > > Thanks. :-) > > Martin >