That's some bad cable, bad contact or interference most likely.
Try it with the PC off. Then silence should be all you hear.
Help, I have recently moved house and have set up my desktop with a new broadband and in general everything is fine. Then I decided I wanted to listen to the radio via the INTERNET and switched on the speakers.
1) I get a throbbing hissing sound and nothing else - the volume can be adjusted but I do not hear the radio just this noise. The trouble shooter does not report ant faults.
2) I use Dragon to dictate and I sometimes use the headphones as an alternative to the speakers. At the moment these seem to be working but the sound is very low. I have tried turning up the volume but I would like it louder - it has been in the past!
Any suggestions please?