Thank you all so much for your help. I've learned a lot.

I think, despite all the recommendations you have made, that the
problem was with the mics - *both* of them, though one to a lesser
degree.

(Jeff, I don't think humidity was an issue. I'm working in a dry, new
building, without major fluctuations in temperature or humidity.)

I spoke to a tech support guy working for Rode in California. He
listening intently to what I described and was very helpful. He
wondered if the "capsule" in one, or both, mics was defective. He spoke
to me about a lot of things - uniform power supply, phantom power,
gain, attenuation, etc.

After a 20-minute conversation, he himself was inclined to think there
was a problem with the mics.

BTW, a few of you wondered if I was using Auto Level Control: I wasn't,
and haven't ever, though it is possible on my recorder. In any case, I
had taken the recorder out of the loop and was getting the "wind"
phenomenon coming back to me through the phones plugged into the
mixer(s).

Finally, I should say that I was very inconsistent about the way I
prepared the two audio clips above - I wanted to post them quickly to
give you an idea. I think I may have run a normalise filter on the
"windy" one (but not on the "pure" one) which explains the difference
in levels. To be honest, at this stage, I'm not quite sure exactly what
I've done, and when. There have been so many frustrating recordings!...

Right now, I'm on the verge of sending the mics back to Rode. They'll
fix them (or replace them) free of charge. I've got to pay the shipping
though...

Thanks again to you all, for your help.

Hugh