Just received my new JCM 800 2203 head with a new vintage 1960 av cabinet. Hooked it up and turned the power on standby. Very noticeable humming sound coming from inside the head. Is this normal? I have a early 90's JCM 900 that never has made any sounds on standby or powered up fully. Can I get some advice before I decide to send it back and go with something else?