so i have an F-1X pre that i sent into alembic about a year ago to have serviced b/c the DI wasn't working and i had some noise complaint issues. after the repair, the DI was fixed but alembic service person said that they didn't find any noise issue. i know that these units have a fair amount of hiss which i tolerate because i love the tone. that is not what i am talking about (though suggestions on minimizing that would be helpful. the noise tends to come and go and i have no idea what causes it. it sounds like very loud microphonics w/ a crackly, cycling type of sound. it is not all of the time, but when it happens the preamp is near unusable. it tends to happen in waves (ie; a week straight then nothing for a month). i have banged around the unit w/ a pen, cleaned the jacks, tried different tubes, and nothing has worked. the unit is plugged into a furman power conditioner. i have tried totally isolated circuits (yes circuits, not individual outlets... worked as and electrician for a few years) so that nothing else is causing interference (ie; washer, dryer, etc). it is not the poweramp or my instrument (the sound happens when the w/out any input plugged in, and stops when the unit is unplugged from my poweramp... i have also tried different poweramps. i love the sound of this unit. i can deal with the hiss. b/c of the awsome tone, but it is becoming usable. any suggestions?