Backround hum issue....

So, I am using a Macbook and a Firewire Firebox for home recording, and today I was blessed with the presence of a nasty hum at varying levels over the course of about two and a half hours.

Knowing that there is an inherent hum with single coils in Strats (I have SD Fender Vintage SC's in the neck and body) I dismissed it initially. However I soon noticed that the hum was notably louder when I shifted the position of the Strat in my lap.

So, out comes my Frankenstein with EMG HB's which should be nearly silent, and yet there is the hum, thought much in lower in volume. After switching between different lengths and brands of cords, thinking that might be the problem, the hum was still there, but clearly not as loud.

Huh? For the record, the last cord I used was the same cord I started with.

I just got back home from a local electronics guru who opined that though the Strat will have hum with the SC's there is something else, likely electro magnetic, that is magnifying this problem.

Has anyone experienced a similar problem like this?

A little more information...
-I have tracked with these guitars for several years, and this is not a familiar sound with either one. They have both been to a reputable luthier for a complete overhaul, specifically wiring and shielding.
-I also moved to another room (to test with a different circuit) with the amp and the guitars, and the problem was still present, and again, the hum would fluctuate with the Strat when I pivoted 180 degrees left and right.

So, strange things are afoot at HTAMs house, and any feedback and discussion would be appreciated.

Gratzi,

HTAM