my ec2a3 did/does the same thing.
here's craig's response to my 6/06 query regarding music coming out of the amp without headphones or speakers connected...
"Electra-Print does not vacuum impregnate their output transformers. The transformer lamentations actual move to the signal, and act as low level speakers. This in no way effects the sound through the speakers or headphones. It is normal, and all of jack's transformers exhibit that anomaly."