In Farfisas extended view you find the NOISE LEVEL parameter. You can use this to control the noise level and even remove it completele yourself, if you wish.
It's the forth knob from the left just beneath the VOICE TUNE section.
The amp has two volumes parameters that both works when the amp is switched on.
And don't forget you also have a volume parameter in the extended view. This pass a a signal to the amp, when the amp is on, and is a master volume, when the amp is off.