New pump and PSC board, system working, pump constantly buzzing ?

Hi Mike,
Thanks for your help, system working fine, apart from the pump is always buzzing ?
Same as before fitting new PSC board, so old one probably Ok, good spare though :-).
I fitted new grundfos 15/50. (not the gledhill one, a bog standard one) is this the problem ?
Pump works fine when system calls for water
Bob

The e7 supply had previously tripped due to a unrelated electrical problem.
so when i restored power the store was cold, resulting in the pump rotating slowly, even when there was no call for water.
This morning, after normal e7 overnight heat up, pump operates normally, when hot water call finishes, after 20 seconds or so stops.
Buzzing was the pump operating at reduced voltage/speed i presume.
silence !

Bob

Is it normal for the pump/ board to buzz after use of hot water? Mine does for about a minute whenever I run a tap.