This is a recent problem that I've noticed since Hurricane Harvey came through a couple months ago. No flooding in the house, but there was 1-2' of water on the street, which did cover the water meter and shutoff (and a couple in-ground irrigation heads) for ~2 days. I'm on city water (i.e., no well, which makes this similar question not a duplicate)
Some time after a water fixture is turned on, the pressure and flow rate will drop for a second or two and then return to normal. It will do this repeatedly, at different intervals. Nothing regular that I can tell. It's like when you have a faucet on, and then turn on the outside hose or sprinkler - that kind of a drop. But it returns quickly, only to do it again some amount of time later.
Sometimes, I'll be able to use the fixture without it experiencing this drop in pressure / flow at all, or I'll only experience one or two drops. Other times, it happens every 30-60 seconds. It happens on all sinks, the master shower, and upstairs tub. Don't know about dishwasher and washing machine. I've experienced it on the outside hose bibs as well.
What could be causing this and how can I fix it?