Transformer hum

[poundy]

What is the main cause and can it be rectified?

 

[rayma]

Is the hum electrical or mechanical?
Is it 50/60Hz or 100/120Hz?
Have you ruled out DC on your power line?

 

[poundy]

I was talking generally realy. If it hums with nothing connected, what would that be?

 

[rayma]

Acoustical hum in a small single phase transformer could be loose mounting bolts or laminations,
or DC in the power line. Try it at a different location to rule out the power line.

 

[poundy]

So it realy depends on what's causing it then, and that would depend if it could be rectified or not I guess?

 

[rayma]

Yes, rectification on it, or on other transformers on the same circuit, can cause DC.
Heavy loads can cause flat-topping.