Heres one way.....
Make sure all of your sockets, ie phone, router, Sky, extension etc.... have filters on them.
Secondly lift your reciever. Dial 0
This will make the dial tone cut out and you will be able to hear if there is any background noise on your line. If your filters are not working or incorrectly installed, you might hear 'white noise' much like if your tv isnt tuned into a channel. This will prob be your broadband.
If its all ok, and you still hear noise, ie a humming noise, it could be an earth problem somewhere in the network. If you hear crackling, could be a contact problem on the network. Contact your service provider for more info.
Hope this helps