I wonder if it's a command or telemetry carrier inserted to run the HVAC? 
Would have to be a pretty hefty carrier, methinks.  If so, a Line 
Conditioner may not be of help.

But you also mentioned the "stringing of some sort of digital cable".  It 
might be time to involve the I-T folks...

Regards,

Mark Durenberger

--------------------------------------------------
From: "Martin Fisher" <[log in to unmask]>
Sent: Tuesday, August 30, 2011 1:07 PM
To: <[log in to unmask]>
Subject: [ARSCLIST] FW: Another AC outlet noise problem

> 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