Australian Car Repair Issues? Ask an Auto Mechanic for Answers ASAP
Surprising your dealer can't give you an answer.
If this is an Auto transmission, I'd say it it is normal operation since the trans would be commanded to downshift at zero throttle AND a brake pedal input.
The random operation would vary on what gear the trans is in at the time versus road speed.
Hope this helps you.
I hope my advice has been of assistance to you.
I would agree with the dealer and say there is no abnormality.