OT: an unpleasant buzz

[info at zoekeating <info@zoekeating.com>]

i'm having problems with a buzzing hum in my active monitor speakers.  
wondering if anyone has experienced this sort of thing and has any  
advice.

- the buzz is a mid range sawtooth wave, with a low @60hz undertone.
- it is a constant volume, i.e. not changed by the master gain
- equal in each monitor speaker
- the buzz is present when the monitors are connected or disconnected  
to an audio input, so even with just a power cable connected, the  
buzz is there
- the buzz is present on all the electrical outlets in my house
- i killed all the circuit breakers in the house except for a single  
dedicated outlet in my studio. then put a lamp on my head (since no  
lights were on), connected a power cable to the monitor, turned it  
on...BUZZ

however, here is one extremely interesting characteristic....the buzz  
is only present between 3pm and 11pm!

the monitors are totally quiet the rest of the day (although i have  
yet to check between 2am and 8am!)
we'll see how it progresses, but i've only been in my studio 4 days  
since being back from tour, and the buzz has been present between 3  
and 11 every day.
i never had any buzz before i left in September

so...methinks it is this thing called "dirty power". i live in a  
ramshackle forest village called "camp meeker", the name pretty much  
sums up the level of infrastructure. regardless, what device can i  
buy to clean up my electricity and get rid of the buzz?

anyone know?

thank ye! zoe