I too am bugged by the constant high frequency whine coming from my Code 50's power section. It has nothing to do with the preamp or patch, but rather the level of the power amp output. It is rather high frequency and constant, and varies a bit when you move your head. But the problem does exist, and it sounds like some high frequencies are not being fitered well by the Code 50 & 100 power supplies or output section. A number of users have now complained about this problem. I have a solid background in electronics and am not a flake! I'm an LA studio musician and this noise is not good for professional recording. I'm hoping it is something that is easily fixable, because I love the sounds I'm getting from this amp.
Can you confirm which firmware you have on the unit.