Im also having this issue.  Beeping set to False but its still randomly does one beep every now and then.  Using a Lan connection, not wifi, incase anyone is wondering.  

It appears to be hashing away perfectly fine.  So I cant work out why it does this random beep.

The manual suggests it beeps when it encounters an error.. but doesnt say what that error is.

I know its not the same beeps as the beeps you get when not connected to a network.