Thanks Dr. Haitz. I hadn't considered a muscle or hip joint pathology, no - I don't even know what those are :) (But I'll look it up)
Just wanted to add to what I said:
(1) There's no bulge or pain when I press on the inguinal area, so I don't think it's an inguinal hernia or similar.
(2) I feel the sensation (when it's there, that is) most when I lift my right leg to put on my underwear/pants (maybe I just need to do a lot of leg lifts?).
(3) I looked at a diagram of the area and my best guess at echo-locating the most common location of the sensation would be probably in the genitofemoral nerve region. I do see that that's right above the actual hip joint, so I guess that goes back to your hip joint pathology recommendation.
Thanks very much for your quick reply.