Thanks, Steve.

I had it apart this evening. It is the transformer. It doesn’t seem to like being fastened down. Removed and put on a chopping board, it is basically silent. Put some bike bar tape under it to damp it, which works ok with low tightening but then putting the top back on seems to load it up again, so it gets a bit louder. Loudest when stood over it but not too bad when in front of it. Maybe some washers and longer bolts on the connection between top and bottom would solve it. Had the option to return it but it is in such good condition otherwise that I have decided to hold on to it, as the dampening and loosened bolts have made it more tolerable.

F80