Monitor High tension PSU question

I have recently replaced the HT PSU on my Hantarex Polo 25" chassis and all is ok... except for one thing which is annoying me - it makes hiss

Is this normal, or the new HT PSU is on the way out as well?

Cheers!

You may have some EHT leakage from the CRT anode to the aquadag (ground) thats the gray coating on the rear surface of the tube.

In the dark you may be able to spot the violet corona spray, probably smell it too, like ionised mountain fresh air.

Remove the cap (after discharging the CRT) and clean the glass. Iso on a rag works well.

A lot of monitors do make whats known as the "15khz squeal". This may be what you're experiencing.

For future reference, the "HT PSU" you're referring to is actually called a flyback transformer.