Juttah,

Trial an error. Eliminate the possibilities. Buy a new faucet and see if it does the same thing. Are all the faucets behaving in the same manner? Then probably it is something happening in your house water system. Does it happen when you turn on a lavatory faucet and let it drip? Is some large water user in the house sucking water elsewhere when this occurs? Are you on a well with a pressure tank or on Municipal water? Do you have a pressure regulator located before your water main enters the house? More info need to narrow the cause down. Aloha

one quick fix to do your watering till you find the cause of the problem is to attach a ball valve to the hose bib, turn the water on and adjust the flow with the ball valve.

Thanks for the leads and the troubleshooting tips -- my indoor faucets don't do this, just the outdoor ones. And one bibb -- the newer one -- is more problematic than the other.

I'm thinking it's the quality (or lack thereof) of the existing bibbs. I'm going to swap one out with something better, like a ball valve bibb or one of those ceramic ones, and see if things improve.

Juttah,

Let us know what happens. aloha