Usually a ground hum caused by an amp/pre-amp interface will be constant in volume, i.e. not change with an increase in volume. The volume control, typically, only attentuates the signal from the source component into the pre-amp. The pre-amps output is typically constant, just as you amps out put is also. So what has changed with your sources, anything at all? Get a cheater plug(s) from you hardware store and start off by using it with each component and see if the hum goes away (its always handy to have one anyway.
Or, perhaps the most certain way is to work backwards. Disconnect all of your components, both IC's and PC's, and run only the amps into the speakers. Any hum? Plug in the pre-amp (IC's and PC's) and hum? No. Go to each source and repeat. You should find it that way. When you do put a cheater plug on the PC to the offending component.
First, disconnect your tv and see if the hum continues. If the hum is still there, then try using the following approach suggested by J. Peter Moncrieff of IAR-80. Use a ground-lift plug to lift the ground on the preamp and other components, execept the amp. Here is his reasoning:
In most installations, you the consumer utilize the grounding lug on the power cord, for all of the various components in your system chain. This is great for electrical safety, but unfortunately it means that your various components are grounded to each other via two distinct paths, via the power cords and also via the signal interconnect cables. This doubling of the ground connection creates ground loops. Ground loops are an undesirable no-no, for several reasons. Ground loops allow circulating ground currents, which create spurious hum and noise. Furthermore, these circulating currents, traveling through the non-zero impedances of the various ground paths, degrade what should be a single reference baseline for ground throughout each audio component and indeed throughout your system. In all audio components, the signal is literally defined by its (usually voltage) level measured with reference to ground as a reference baseline. If that ground reference level is different among different components, or among different parts of any single audio component, then the whole reference baseline is corrupted, and the audio signal is perforce similarly corrupted. Thus, ground loops effectively corrupt and degrade your audio signal. Sonically, the stereo imaging suffers, and the music can become more veiled and less pristine and pure. - J. Peter Moncrieff
Just as an aside, I once discoverd a hum was created by a faintly corroded ground wire coming from an amp cicuit board that attached to the amp chasis. Hum problems can be very, very vexing.....