As far as I'm aware if one party disconnects but the caller doesn't the system checks for a voice signal on the line, and if there isn't one it disconnects after a short period of time............you should then get the 'hooter' down the line to tell you to replace the receiver.
I may be wrong but I think that noise occurs when a receiver have been knocked off the phone and yet no number is being dialled. There may be a timeout on a call you forgot to end, but I am not aware of it.