Pulsing water/knocking pipe

[Jimbo]

My cold water tap in the bathroom has started pulsing when it's first turned on. This is accompanied by a pipe knocking somewhere in the depths of the house. After a few seconds, the water starts to flow normally and the knocking stops.

Can anybody suggest what might be causing this problem? Is the pipe knocking because the water is pulsing, or vice versa? And if the former, why would this suddenly start happening? The other cold taps in the house are okay.

Thanks for any advice

 

[masona]

Have a look at the taps washer first to see if it come of the spindle