A possible cause is, as has happened to me:
Parked on gate at night awaiting de-icing.
Voice on i/c: "Let us know when you're ready to start."
Bas: "We're waiting to be de-iced."
VOI: "You've just been de-iced!"
No warning and with APU bleeds open. Fortunately no ingestion.
I learnt about flying from that.