I came across your post at about Rocktron's G300. I have one of these and the sound is incredible. However, this unit also create lots of hum on most of my presets, especially ones with clean channel. Even if these are factory preset.
I did email Rocktron but they seem dont have answer for this.
I wonder if you have any idea that can help me eliminate the hum noise (??)
Your help is much appreciated.
The G300 is pretty cool. What guitar & pickups are you using? I found that using hi-gain settings with my Gibson '61 VOS SG caused a lot of feedback. I believe it was due to the historical Burstbuckers not being as shielded in comparison to Burstbucker Pros in my Gibson USA LP Std. Is your guitar equipped with single-coil pickups or P-90 style? If so that could be your problem.
Since most all of those presets have some type of EQ and amp simulator setting on them you should make sure that your G300 is set for going into the amp without the speaker emulation. Lastly you should also check out the HUSH noise gate setting and make sure that you are getting the type of response you need to get.