We have a BT Versatility System and one of the extensions is playing up, all others are fine but from this extension you cannot transfer calls (and yes I have checked the time break recall settings) and there is a beeping intermittent dial tone when you pick up the handset as if there is something programmed.  I've tried all the reset codes, tried resetting the system, warm and cold and it seems to make no difference, I've tried a different phone in that extension and I've tried changing that extension, nothing seems to work any ideas ?  it also rings back one ring when you have finished a call