Noisy heating

Can anyone shed some light on my heating noise problem? My system is fully pumped with 3 port valve, header tank, 8 radiators all with TRV's. I understand one radiator should not have a TRV in-case all the valves shut down, therefore one is set fully on. When the system is heating hot water only or HW and radiators it's fine, no noise. If it's only pumping water to the radiators there is a loud whooshing sound from the pipe work around the pump, this noise gets worse as radiator TRV's close down. I assume this is something to do with flow rate being too high, I've reduced the pump to it's lowest speed and I'm sure there's no air trapped in the system, also all lock shield valves are fully open, but to no avail. It's confusing because a friends heating system (very similar setup) is silent even with only one radiator on.

Shouldn't the system be almost silent even if only one radiator is on? Would an automatic bypass valve solve my problem?

Dan

I've got the same problem but on the HW, every 5 mins whooshing !! My system is a little old and the bore sizes are down due to oxide build up. When the system is flowing through just HW as the pressure is higer than it used to be due to restricted pipework, you get a steam blast up the vent to the f&e cistern in the roof. I'm going to try a double dose of x400 for 2 weeks then drain and fill with x100 if no good I think a proper system flush may solve it. In my case I can't see it being poor plumbing (position position of feed and vent from f&e cistern can cause it) as it would have been like it since day 1 and someone surely would have fixed it ! Plus the vent is behind the pump. Also if you turn the stat down on the boiler it prevents the overheating when just on CH in your case.