Vertex VXA-150 Pro V handheld radio question

I just got a new Vertex VXA-150 handheld transceiver and wonder
if anyone else who has one can answer a question for me.

I programmed in two frequencies and set the radio for "dual
scan" The secondary frequency was very active, but it was
difficult to hear on dual scan. The broadcast was interrupted
every second or so with a short burst of static hiss. It sounded
like the radio was frequently re-tuning itself to the primary band,
listening, playing the static it found there, and then switching back.

Does anyone know if that is the expected behavior? Or is
my radio defective and in need of repair?

If it's expected, I'll keep the radio anyway since I like the
size, sound, other features and price. But if this can be
fixed, I'd like to get it fixed.

Thanks.