If one zone is already active and another one starts calling, it sounds like the blower ramps up to provide the additional air flow before the damper opens and directs air to that zone.
The result is that when we are downstairs and the upstairs starts calling, there is a brief period where there is a lot of air moving through the downstairs vents (very loud "woosh") before this additional air is directed to the upstairs vents and the downstairs vents are quiet again. The system has done this on both air conditioning and heat.
Is this normal? Thanks!