What we are thinking, is that the pump pressure is so high, it is forcing the TRV to lift of it's seat slightly, making the noise. Dropping the pump speed, might be all it needs, to fix it.
That was my thought, although was going to point at the by-pass valve. I know with TRVs we should have a by-pass valve, and I also know I can't find one on my own system.
The basic system is flawed in many ways. The idea is the return water is monitored and when it gets hotter the boiler output is reduced to keep it cool enough to gain the latent heat. To do this it needs a by-pass valve, so when the TRVs close, there is a route for the return water.
But before the condensing boiler, we did not require the return water to be cool, so neither did we require TRVs nor by-pass valves, so we often end up with a compromise system where some but not all bits have been updated. Some boilers have the pump and by-pass valve in the boiler, and some they are external, so mother house I found had two by-pass valves, one in the boiler and one outside.
To be frank there were a load of errors made fitting her central heating, it was done under a government scheme, and it seemed the installers did not have a clue.
I look at my own central heating, the boiler is clearly far too big to heat up one radiator, but if I have Wiser heads on every TRV then at some point, it must have heated every other room, so there is only one TRV calling for heat. So I have not fitted Wiser heads on every radiator, and I have the non-linked TRV heads set a little higher to the linked head (Wiser) so it does not end up only heating one radiator. And in the living room, my TRV heads are set higher than the wall thermostat. Same with hall, TRV is set higher than the wall thermostat.
It is tempting to say there should not be a TRV in a room with a wall thermostat, but that is no longer true, it depends on the type of TRV head used, some heads are designed to work with wall thermostats, like Wiser and Kasa, so can't make a sweeping statement like that any more.
However, it may also be as simple and the lock shield valve not set correctly. The correct way to set uses a differential thermometer which most people do not have, however half of my TRV heads show both target and current temperature, and the current should not, unless there is another heat source, exceed the target, if it does, the lock shield valve needs closing a bit.
TRVs take time to open and close, and without the lock shield valve, the radiator would get stinking hot, before the valve has time to close, so we need it to take around 15 minutes for the radiator to fully heat up, as every Saturday when my TRVs exercise to stop them sticking, at midday, I hear the motor run for around 5 minutes fully opening then fully closing the valve then returning to the setting, it also recalibrates the head as well as exercising the valve to stop pin sticking.
Since I use programmable wall thermostats, as the room temperatures change through the day, clearly also need programmable TRV heads, and the old wax head is not programmable so is no good for me. I have a mixture, eQ-3, Energenie, Kasa, and Wiser, each slightly different. And I will admit the cheap bluetooth eQ-3 heads only show target temperature, what can one expect at £15 each? But to set lock shield valve, I just swap them with one that does show both current and target, then once set, swap it back.
