Hmmm... from what I can recall on the flight deck visits I've had in the Dash, they set the cabin altitude to aerodrome elevation at around 1500ft so that the pressure is equal when the doors are opened. If there is a large pressure differential between the cabin and aerodrome elevation it may cause the hissing.
Id say you have issues equalising rapidly, its ok at a slow change but the rapid change may be whats causing the pain.
Try PM'ing 'Link148' I think it is, as he is a Dash pilot and may be able to offer advice.
Otherwise ring up Dr Baldwin at PM and see what he has to say, he is a legend when it come to aviation medical things and always great to chat too. He is found at
www.flyingdoctor.co.nz~KAG~

This time it happened in a Bech 1900D. In the Dash it happened a lot higher, but we also flew an instrument approach so they may have set the cabin alt to aerodrome elevation a little higher up. In the Beech, we were on a visual approach.
Thanks for the advice. I might see if I can chase up Dave Baldwin and see if he has any suggestions. It feels wrong being me and also dreading flying, so I'm keen to sort this. Next flight I take I'm gonna try chewing airwaves from top of descent as they have natural decongestants in them. It still sucks sitting there as a passenger feeling all tense as you anticipate pain coming on - hardly what you'd expect an aviation enthusiast to look like as a passenger!