Check out the ISP Technologies Decimator ProRackG. The guy who invented the Hush quit Rocktron and started ISP - then took the technology way further. It is unreal how good it is.
The major part of the noise from an amp is from the preamp raising the noise floor (hiss and hum on your dirty channel), therefore noise suppressors are most effective in the effects loop (fx send = preamp out .... fx return = power amp in). In other words it is cutting the preamp noise out and leaving only the noise which is inherent within your power amp. The only problem with noise suppressors other than the ISP is that they will chop off your clean channel's signal because the threshold you set is going to be JUST above the noise of your dirty channel. The ISP won't because it works off of your actual guitar signal which then triggers the noise suppressor that is in your effects loop.
Anyways, I'll stop pushing ISP on you. haha pretty much try putting it in your effects loop and yeah..sweet. haha
Greg.