making noises in my transformer

So, i have a little issues that might need extra hands to get it right, last night I did power up my 300 VA toroidal and it is making a quiet buzz.
On smaller toroidals this usually means there is a short somewhere right, but in my case the buzz persists continuously with the transformer bolted down, or with bolt removed, at a different location, and with bridge+filters connected or not.

Does anyone know what might be causing this ?
 
Many possibilities: a typical (but non-limitative) example: a hair-drier operating at half-power thanks to a series diode.
Many cheap soldering irons also use the trick.
The problem does not necessarily originates from your house: any neighbour on the same circuit could cause it
 
So, i have a little issues that might need extra hands to get it right, last night I did power up my 300 VA toroidal and it is making a quiet buzz.
On smaller toroidals this usually means there is a short somewhere right, but in my case the buzz persists continuously with the transformer bolted down, or with bolt removed, at a different location, and with bridge+filters connected or not.

Does anyone know what might be causing this ?
Does the unloaded transformer heat up excessively when powered for a while? Also, toroidals are sensitive to any DC component in the AC power because the magnetic paths are so good at what they do. Also, excessive capacitance on the rectifier output can cause that due to extreme current spikes on the charging cycles of the AC input waveform.
 
Okay, yes i am making some more research but there are two smaller toroidals (50VA and 80VA) which are not making this buzzing noise, unless you pull like 90% of their rated current. Also, there are two fluorescent tubes transformers which are making similar buzzing noise, I suppose for different reasons. The soldering iron station also buzzes when it heats. I presume all those symptoms are unrelated.

The buzzing is mechanical, something is vibrating.

Could it be the core is fragmented? Could it be there is a few loose windings ?

In either case could this mean the transformer is unsafe and a potential risk?