Patrol dash noises

OK, I know GQ's have some dashboard rattles as standard, but mine hasn't been too bad - until recently. It has developed a loud rattle which sounds like it comes from the right side and fairly high up. It sounds more like there's something loose and flapping and only comes in when I'm doing around 100 kph or more. Sometimes bumps will affect it but not always - almost appears related to speed/wind. I have pulled out the covers under the wheel arch - nothing found. Looked everywhere underneath in the vicinity - nothing. Stood on my head looking up under the dash for ages - nothing. Almost at the stage where I pull out the instrument cluster and also the air intake grille in front of the windscreen to see what I can find. I don't think it's in the heater as the fan makes no difference at all. It really is a fairly loud clunk/flapping noise and very annoying. Can't "feel" anything by touching the dash, door, floor etc either.

If anyone has any bright ideas or has gone through a similar scenario - PLEASE let me know before I run off the road trying to find it!

Thanks folks...