The NB9 and NB9W may make a clicking noise every 15-20 seconds.
This noise is not a defect in the unit, and is simply a part of the unit's design.
If you do not use the VoIP features of this unit, login to the device using it's IP Address (by default: 192.168.1.1). Go to the "Voice" section on the left, then click on "SIP".
Make sure the box entitled "Use SIP Proxy" is UNTICKED.
If you are using VoIP successfully, you should not have this problem.
Some ISP's have TICKED this option by default on the unit's that they provide.
More information: When the "Use SIP Proxy" option is TICKED in the Voice, SIP section of the NB9 / NB9W, the unit will constantly attempt to register to the SIP Proxy servers that have been specified.
If the registration attempt fails for any reason, the unit will switch the 2 Phone ports on back to the PSTN line, which is the normal Telstra telephone line. It is this switching process that creates the clicking noise.
When VOIP is working properly, ie: When Voice calls are able to made successfully, the clicking noise does not occur.
Similarly, if you do not use the VoIP function, and you have the "Use SIP Proxy box" UNTICKED, the unit will not click constantly.