Just noticed this over the past 1-2 weeks:
When I turn on the pool filter (6 y.o. Pentair DE thingy) a cloud of DE blows out into the pool from the returns. It is a 2-4 second cloud accompanied by alota air bubbles too. Then, it all goes away.
I've looked for leaks and can't find any.
I think I see more air in the pump clear big cap thing that you open to get all the big leaves and stuff out of the strainer. Can't say for sure, as there always seems to be a little bit of air trapped at the top of that clear plastic dome, but maybe more air lately?