Hi

You can get a stethoscope for less than 10€ on Amazon to listen to your pipes.

Candidates are heat pump compressor, fan, circulator or circulators if you have several.

Then turn off circulators one by one, then turn off heat pump with the thermostat. It'll probably stop the compressor immediately then still run the internal circulator for a few minutes. Same when it starts, the circulator will start then run for a few minutes, then the fan, then the compressor starts. So you can find the culprit depending on what's on when the noise appears.

If vibration comes from the heat pump and travels through pipes you can put in a flex hose in between to stop propagation. Another culprit can be a bit of junk stuck in a circulator impeller.

Perfect this looks like Easy MCS format: so they have design you for 50 flow at -3. So what I advised you 47at -3 is a good start. 

@cmartinbwmba

if you find this to warm in the colder in cold winter just reduce the 47 to 46 and so on, if you find it to warm when outside is spring 15Deg C reduce the 27 to 26 and so on. if you find to cold in either season do the opposite.

I made you a new black line at 57 thats in the middle of 4 and 5 and then 2 lines showing the external temp and 2 pink lines showing the flow at temp. 

amazing thanks for your help!! Yes we use rads

Great, rads are good, the curve i gave you is more of a rads design. Try that and see how it goes.

@cmartinbwmba

if you find this to warm in the colder in cold winter just reduce the 47 to 46 and so on, if you find it to warm when outside is spring 15Deg C reduce the 27 to 26 and so on. if you find to cold in either season do the opposite.

I made you a new black line at 57 thats in the middle of 4 and 5 and then 2 lines showing the external temp and 2 pink lines showing the flow at temp.