Machine gun that shoots paper bullets?

I was walking yesterday afternoon in a fairly busy suburban commercial area. I took a turn by a car stopped at a stop sign. When I was about five or 10 feet away, suddenly I heard a noise it sounded like rattatatta like a machine gun, though not loud like firearms. I was struck in the back with several somethings very lightly… Just enough to feel it, not enough to remotely hurt at all or even sting. Didn’t mark my clothes. I looked down on the ground and didn’t see whatever the projectiles were. I looked at the car and didn’t see anyone, just an open back window. Then they took off from the stop sign.

Does anyone know what they were using?