"Brian Gaff" wrote in
:

Our studio has a radiator like that, we call it hissing sid.
My guess is that its turbulance in the hot water squeezing by the
valve or
tap or whatever is adjustable.
It needs a very delicate touch to get it just right!
Brian


Of course - the noise is caused by it beginning to close - or open so in a
way it is something that should not be avoided by turning it up or down.