You have actually brought up a very interesting question….. I bet there are very few engineers who have had experience of ‘magged up’ microphone transformers!
High quality transformers are made with laminations of different materials; partially soft iron and partially ‘Mu metal’. This material magnetises easily and retains its magnetism. Plugging in a microphone with the phantom power turned on can momentarily cause a current surge in the transformer which magnetises the core…. the transformer then operates like a microphone! Usually this is not a very serious problem as the microphone itself damps out the microphony, but unplug the mic and it becomes very obvious!
I suggest, ignore it! de-magging the transformer is not an easy process and apart from ‘ringing’ when there is no mic plugged in, it should not be a problem.
On the other problems, I would have to look at it to comment. 