class d airspace

About once a week I'll hear someone contact my tower (class D) with a radio call like this: [PART 1] "Pilot: DuPage Tower, RV 123AB" "Tower: RV 123AB, DuPage Tower" <Crickets for 5+ seconds> [PART 2] After long, awkward silence on the channel... "Tower: RV 123AB, DuPage Tower, say request"...