Noisy cold water pipes

[Lyds]

Hi, I live in a flat at there is a high pitched monotone noise coming from the water pipes which come into the flat from the loft. The pipes also go through the floor to the flat below. This has only started today, there is no water running, and the guy downstairs is out so he's not running taps. It's intermittent but has been going on since I got home over an hour ago. I don't have a boiler, just an emersion tank, and it's not coming from there. Could anyone give me an idea what might be causing it? Is it something that needs urgent attention, apart from the fact it's seriously annoying!
Any info would be great, and much appreciated.
Thanks
Lydia

 

[ShaunCorbs]

might be a ball/float valve (toilet cold water tank etc)

 

[plumben]

As above, Most likely to be a ball valve either in a cwsc or toilet, just needs a new washer, if its a rented flat contact your landlord/agency and have them send a plumber out

 

[Stigster]

Is there an overflow with water coming out of it anywhere?

 

[ShaunCorbs]

or any dribble of water coming into the toilet pan