noisy water system

[canit]

When I flush the toilet, at the very moment it fills to the top, a loud humming noise sometimes sounds starting low then to a loud hum then after 5 seconds or so it stops. Also turning of the taps can cause a lesser noise shorter in length.
This does not always happen - maybe once or twice a week then for days no noise.
Water pressure is constant but since we had a new water pump fitted this problem has started.
The noise is not the 'water shock'? which is more a banging noise. Any help?

 

[ChrisR]

Common. Changing the washer will cure it. Changing the whole valve for a brass one may be better as the plastic ones seem to be more susceptible, but a washer will last a long time!