Oops, I am embarrassed to admit that my diagnosis was wrong.
Upon further investigation the noise is coming from my Anthem and/or LG projector.
I found out when I did not hear the noise when my LG was switched off.
It only occurs when the Anthem and LG are both on and connected with HDMI.
I am still investigating what the cause is.
Anyway, I have learnt some new things from this thread and I am still going to swap out the amps. I will get a pair of Hypex NC500 based amps on Saturday. They are supposedly the prototypes for the Taiko Audio Kodo amps.
Members here will not be surprised that these amps (basically a stock NC500/SMPS 1200A700 build looking at the inside) retailed for EUR 4.000 each!
€4000 Ultimate Audiophile Performance Class D Power Amplifier based on the Hypex Ncore NC500 amplifier module...
I was not swayed by the fancy language about the design, but by the low price I could get them for.