[asterisk-users] Buzzing / Humming Noise

[adamk at 3a.hu]

To me sounds like an electrical interference.  I assume you're not using 
PoE.  Try plugging the phone to someplace else and see if the noise 
still appears.

Use wifi and battery powered cellphones with SIP clients to rule out

- pbx
- parts of the wired network

To confirm it's an electrical interference, try to schedule an 
out-of-hours test when you switch off all PCs, fridge, whatever you may 
have in the office.  I'm guessing the buzzing sound will not be present. 
  Start switching PCs on one by one while listening, the buzzing sound 
will return at a certain power consumer device, or after having a 
certain number switched on.