IF you can just lift the speaker out of the cabinet and maybe use temporary wires say 1 metre long to get it OUT of the cabinet, then monitor the humming.

Marty

OK, gone a couple of steps forward this morning.  Pulled out speakers out of front display panel (very sad looking speakers).  Went down to Jaycar and had a look at what they stock.  There were some nice 4" speakers, but the cone would hit the grill, so no good.  They had some cheap n nasty speakers almost identical to the ones that were in there (4" 4ohm).  I guess cheap crap from 20yrs ago vs cheap crap now, now would probably be a bit better.  At $3.80 each it was worth a shot.  Put them in, a little better, but still humm.

So, keeping it simple I disconnected display speakers, tried again...Little better, but noise still there.  Disconnected cab speaker...Noise still there. Soo, this makes me think that the transformer is to blame.  Its on silicon at the moment, but maybe not enough.  I will try pillow and see if that helps.

Do transformers buzz on their own without vibration?