Fluidmaster concealed cistern bottom entry - experiencing a 'thud' noise

[Cruise]

Hi, please can someone help?

I had a new Fluidmaster concealed cistern bottom entry fitted recently. Model is Fluidmaster 400UK bottom inlet valve with dual flush pushbutton.

I am experiencing a 'thud' noise after water flushes away from pan. Does anyone know whats the cause? Is this due to bad installation? as my previous cistern 10yrs old never had any noise from it considering this is a brand new cistern.

Thanks in advance!

 

[BLOD]

Hi Cruise,
its probably the flush valve closing after the cistern has emptied all its water that you can hear, you can normally hear a small thud when a cartridge type flush valve closes.

 

[PlumbBobBob]

i agree, probably the flush valve closing as BLOD says