Expansion valve making pulse vibration

[HenKri]

I have a 9 kw liquid/water heat pump. Refrigerant is R410A. Because of a broken pipe i changed the condensor plate heat exhanger. After the change, the expansion valve has started to make pulse vibration/noise 5-10 minutes after startup. When the vibration occurs, i can se some bubbles in the sight glas.

The water pump for the evaporater have 3 speeds. There is less vibration at the lowest speed, and if i run the pump on full speed, the vibration is constant, not only pulses.

I tried to increase the superheat, but it did not solve the problem.
What can the reason for this be? Can it be to much refrigerant?

[RANGER1]

HenKri,
Does the pulsations mimic discharge pressure.
Have seen it happen with a different setup than heatpump where PHE condenser water control valve was modulating.
If system overcharged, would it be seen by high than normal discharge pressures.

[ntfreezer]

which brand of the expension valve you used? danfoss valves maybe have this problem I have met once.