Do all toroidal transformers hum?

Yes, it is quite normal. If you cannot hear it unless you are that close, forget about it. On big amps with modern transformers toroidal or iron core, you get humm. Many manufacturers cover transformers to reduce audible hum or soft mount them to do the same. Top quality transformers do not hum.

Thank you all for the responses, so you think most of the amps carry mediocre trannys?

Regards

The question is, does the slight hum have any practical effect. While the best transformers may not hum having one that makes the slight noise yours does does not mean that it is a bad transformer or that performance is necessarily bad. There are components where everything has been selected with cost no object and they are very expensive. Good designers select components that will do a good job at a reasonable price, if you are happy with the performance otherwise don't worry.

Hum is just 60 Hz and 120 Hz vibrations within the transformer. There is probably a subtle effect of these vibrations on the ac wave, but you are right it has little effect. Yes companies frequently buy marginal transformers to assure a price point. You get what you pay for.

Thank you Stanwal and Tbg, that was informative. The funny thing is that I had Denon POA 2400 (200W/channel) not a sign of hum, but the DK does have a faint hum. I guess I have to live with it as it's not audible 3 inches away from the amp. The Denon had a cheap 2-pront (no earth) power cable, do you think the grounding might be an issue? I had a B&K MC 101 Pre-amp with a IEC power cable and that had a hum too.