Occassional itching or "flashing" on gravel?

It seems it's not uncommon for an individual fish in my tank to go through a
few days when they will occassionally quickly rub themselves against the gravel
or other objects in the tank. It looks as if they're quickly scratching
themselves, possibly the gill area, and I think I've heard this behavior
referred to as "flashing"?

It's not a constant thing, and the affected individual seems to discontinue the
behavior after a few days, altho another may pick it up. Whoever is "itchy"
that particular day may do it once or twice during maybe an hour of
tank-watching. It seems a bit more common for new arrivals than for fish who
have been part of the community for a while. No signs of ich btw.

I know that constant behavior of this type can be a sign of various diseases or
other problems. What I'm wondering is if this occassional behavior indicates a
problem or is usual. New arrivals that pick up this behavior on introduction
to the tank seem to get over it in a few days, so I'm wondering if it's a
period of adjustment to the water type, or a sign of a more serious problem?

TIA for any advice -- Jim