Any birders out there?

Any ideas on what type of bird was in my tree today?
It was a small buff bird, smaller than a mockingbird (whose regular branch he was on and subsequently chase off of), no obvious brightly colored plumage, breast is lighter fading to white at the throat and he/she makes a call like “Jibbedyjibbedyjibbedy – jib”. Any ideas (and did you try to make the call out loud)?