Hi,
Looks like Ive found the problem now with the heating. Fixed weeping valves on the towel radiator and bled system again - cavitation noises still evident from the pump and sound of air moving around the house still evident.
Anyway, noticing that my hall was a bit cold I checked the radiator valve on the hall radiator, noticing it was only 1/2 open I opened it fully. From then on the noises got a lot worse.
So I turned off this radiator and the noises stopped! At first I thought the problems were isolated to this raditor. I then experimented by turning another radiator off and the hall raditor back on - no noise.
Then turned all radiators back on - noises now evident again. Bottom line is that by turning off one of my radiators the noises seem to go away. I wonder if (since the installation of my large towel radiator - prob. 4 x capacity of the radiator it replaced) I have overloaded the system?
CM.