Very strange..I thought I wrote a follow-up last week to your responses, but it isn't here. I'll try again.
The transformer noise problem was reported to me by a couple of electricians who had replaced the noisy transformer, only to note that the new one acted exactly the same as the old one. That's when they noted that the ground electrode connection was missing. Once it was properly grounded, they claim that the transformer ran quieter. Do you suppose this was just wishful thinking?
All I can think of was that there might have been some preferencial capacitive coupling for one phase, and it resulted in some magnetic imbalance...creating excessive noise...but I seriously doubt this is the case. I'm open for some enlightenment here....I would hazard a guess that the electricians just didn't let the new transformer warm up enough, or that the loading was different (as you suggested Bjarney) and they didn't notice that fact..
I haven't heard of the "cast coil" type...I'll keep a look out for them now, Nick.
