It can indeed drive one nuts.

I'm not convinced that the HD500 and the incredible ZT Lunchbox are faulty in design - Line6 doesn't make bad products (even if some of us think they sound bad, that's not the same thing), otherwise they wouldn't earn their various safety standards labels (one hopes!).  I think that as guitar equipment designs shift from traditional to whatever new technology, or ideology, there's going to be a need for the musician to be more savvy.  Transformers in traditional designs are no longer present in the front of the signal chain, so passive guitars are exposed to more of the wonders of electrical circus floating through us all.  I'm MUCH more aware through this experience and it's actually already made me take more control - in a good way - of my over-all tone.  So, in a weird way, I'm grateful for these problems, as it's thrust me into learning mode.  Never a bad thing for anyone at any stage in life, yeah?

Numb, your AC line isolation transformer, what brand and model is it, if I may ask?