Fender Twin Amp buzzing coming from circuit board!?

[disorder]

I recently repaired a Twin Amp (NOT the '65 reissue, this is the tube twin with adjustable bias on the back panel) and 25w/100w switch. Single input on the front only.

The issue was a faulty B+ resistor.. the 1k Flameproof was faulty so I put a new one in with some addition clearance between it and the PCB and the amp sounds fine now. However.. there is a buzzing coming from the circuit board. The buzz originates from the side closest to the power transformer. Its louder at the 100w setting than the 25w. Also the power transformer gets pretty warm after jamming on it awhile. Not burning hot though. Is the buzzing noise/warmth a concern? I chop sticked around the right side of the PCB but it didn't stop or alter the buzzing. Its similar to the buzzing coming off power lines.

[faman777]

I've seen that on a couple of newer Fenders recently, not a loud buzzing just a kind of vibrating and very low volume buzz. It turned out to be the power transformer was vibrating and after a bit of research found out that some transformers do this normally. There was a name for the phenomenon, but I forgot what it was. I found it by switching the amp off and waiting a couple of seconds and then turning it back on while touching the area where the power transformer was. If I'm remembering correctly it didn't matter if it was in standby or in play mode, the vibration was there either way.

[Enzo]

Oh, "magnetoconstriction" or something like that.

[Jazz P Bass]

From Wikipedia: Transformers
"Magnetostriction
Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This produces the buzzing sound commonly associated with transformers,[30] and can cause losses due to frictional heating.
Mechanical losses
In addition to magnetostriction, the alternating magnetic field causes fluctuating forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the buzzing noise, and consuming a small amount of power."