I have 3 sets of Sennheiser G2 portable setups running into a Shure FP33 mixer....
One of the receiver units "Clicks" like a metronome about every 1/2 second at normal voice o/p signal level ....BUT ONLY when the receiver is turned OFF.....

I have changed the 3.5mm > XLR leads around, I have changed it to various inputs of the mixer, the mixer doesn't have phantom or T powering active, I've tried it on other mixers and it still does it, and I've tried it at many locations and it still happens.

When the receiver is turned ON every thing works fine... the clicking is ONLY there from this 1 receiver and ONLY when turned OFF.
At the moment I'm unplugging the unit from the side of the mixer when its not being used to stop any possibility of leakage into a mix.

Any suggestions?

Any suggestions?

Contact Syntec (http://www.sennheiser.com/sennheiser/home_en.nsf/root/0service-partner?Open&country=Australia) in Australia (the Sennheiser Main Agent in Oz) - they will sort it for you.

Reminds me of that old joke:

Patient: Doctor it hurts when I do this (raises arm).
Doctor: Then don't do that.

Just kidding, I'm sure it's annoying since it seems your operational needs have dictated turning off your receivers at some points during working. It's very rare that my receivers get turned off except when packing up.

I assume you've also tested it with the battery out? If removing the battery still results in clicking then it's some passive artifact of this receiver.

If it disappears after removing power from the RX, then it must be generating the click and could indicate some more serious internal problem.
Have you contacted Sennheiser?

I guess I'd assign that RX to be the one least likely to be turned off during your recording if you can't be without it. Otherwise I'd contact Sennheiser and see if they've heard of this before and want it sent in for service.
Or upgrade to a G3 and keep this unit as a spare.

Good luck with it!

As it makes the clicking noise when turned OFF, I wonder if the cause is phantom power related, and the click is something charging then discharging with a click, and then repeating over and over? Turned off, the receiver should be totally silent. If it isn't, then it's getting power from somewhere, and maybe 'bunging' 48V up it's output is causing the output electronics to object, loudly!

The OP said his mixer doesn't have phantom power on but it's possible (since that Shure mixer can output mic level signals) that the output of the mixer is connected to a camera or recording device that's outputting phantom on its mic input. This could also cause odd behavior in the connected receivers if there is a circuit problem.