02-26-13: Fromunda
Fosgate sig was the last addition. But I believe the hum was there before as well.
Was your previous phono preamp a tube unit too? Hum is not uncommon using tubes in high efficiency systems. Try a SS phono stage and see if the hum goes away. It doesn't have to be an expensive one, you can find a SS phono preamp for under $100, it should at least let you know whether or not the Fosgate is the problem.
I have something like this as a back up to test for issues like this. In my experiences, I prefer solid state for very low level signals like vinyl. Tube line stages and amps are great, but you have to be careful with tube phono stages. The more efficient your speakers are, the more likely you are to hear tube artifacts in low level amplification.