Any noise from your guitar/cable will be amplified by a compressor because the comp is essentially turning down the louder stuff, then turning everything up to compensate. Start by making sure your guitar has as little noise as possible with shielding, efficient wiring, etc. and use a shorter, high quality guitar cable. It's also possible a buffer at the front of your signal chain would help, but if your comp is the first pedal then it probably won't make a difference. Next, some circuits are noisy due to cheap components or poor assembly. Some circuits are inherently noisy. Dyna style comps can easily add noise, especially the cheap ones. I'm using a TC Hypergravity, no added noise. It is digital, though, which some folks don't like.