Hehehe... dude!
The compressor, when you turn up the "sustain" or compression, you get "more" noise... its normal.
What you are doing is compressing hte sound, bringing up the volume of the soft sounds (e.g. hissing, humming) and bringing down the volume of loud sounds (adding a "ceiling")... hence, the "noise".
Its normal.
If you want more sustain, work with the guitar first... setup, strings, etc etc... or use an Ebow, or install a sustainer.
You want more sustain on clean or distortion?