Shower pump squealing

Hope someone can help with this.
I recently fitted a whole house pump to our vented system which all went ok. This is pumping hot and cold to all outlets except toilet, washing machine and kitchen cold tap which are on mains. Cold has it's own feed from cold tank and hot is connected via an Essex flange. I primed the pump correctly as per the instructions and have no problems with air in the system.
If the pump is allowed to operate with no restrictions, like having the bath taps on full, it is very powerful and surprisingly quiet. The problem is, when the taps are only half open and restricting the flow, the pump makes a loud squealing noise. This stops as soon as you open the taps fully.
I'm hoping this is not normal as surely everyone who has a pump fitted doesn't have their taps on full blast all the time.
Any advice received is appreciated.
Oh and pump is a ST Monsoon 1.5 bar twin.
Cheers all.

You have a hydraulic powered oscillator and the frequency of oscillation may give some clue as to the size of the loose part that is vibrating, with smaller pieces giving higher frequencies.
Maybe it's cavitation.

Thanks for the reply.
Not quite sure what you mean though, are you saying that there is something loose and oscillating at a certain frequency in the pump?
Thanks.

Yes, maybe some small part is loose.

If you post the noise on YouTube many more people can help diagnosing this.

Ok thanks for your help. Have contacted the pump manufacturer to see what they have to say.
Cheers.

si345 said:

Ok thanks for your help. Have contacted the pump manufacturer to see what they have to say.
Cheers.

Click to expand...

Good. Contacting the maker seems to be last thing most people do. Half the makers I e-mail don't answer, out of arrogance or on 'advice of counsel' or because time spent dealing with buyers' questions is money out of their pockets.

Whats the make and model