Baxi boilder pressure drop and then returns to normal?

[Claire1999]

Hi, I have a baxi duo tec 24 and its started having some weird behaviour. When I run the hot tap the pressure drops and it making a really quiet high pitch whistling sound. The sort of sound that would drive teenagers and dogs mad. No error codes and all work fine.
Just want to know what checks I could do before calling someone out to have a look or it someone has any idea what it could be ?
Thanks

 

[jeff the gasman]

The slight pressure drop is normal. It’s the effect of the pump.
Make sure pressure is at least 1bar or 1.2 bar when cold.
Noise could be pump, fan or hydraulic noise. An engineer would identify the source!

 

[Stadan20]

Noise will be the inlet cartridge if I was to put money on it , very common with this model