Do all toroidal transformers hum?

Thank You all for the great advices. Just want to make sure that the hum is not going to damage anything (I'm new to this stuff,so please pardon my ignorance). The DK does have covers on it's transformers.

I would not worry about hum that is audible only two inches from the top of an amp. Virtually any toroidal transformer, even of the best quality, will buzz to some degree if the DC level on the AC power line is high enough.

A friend who suffered with this problem, only to a much greater degree, told me of this thread. Most of what has been said is fairly accurate. DC on an AC line in excess of 1 volt makes a toroidal transformer hum. Also, as has been pointed out, most transformers hum - magnetic flux in action. However, when it is audible it is excessive. It really has to do with how the transformer was wound. In addition to power conditioners with huge toroidal transformers, we make a DC blocking power cord that has thus far been effective in eliminating hum in the excess DC situations. I am not here to hawk my products, but if you have an interest, just ask.

Thanks Gbart, the fact that my B&K MC Pre-amp with external power supply also had a faint hum (again when I put my ear to the power supply), does that indicate a DC presence on the AC line?

Dstandard, where can I find your product catalog?