I get a couple of years' use out of them and then my AirZounds die. Is this a common problem?

The symptoms this time and last were pretty similar. I find that the bottle is pretty squeezable and has lost air. If I pump it up a bit, I might get a faint AirZound-like noise out of it, but then that's it. All that happens on subsequent activations is the whishing noise of air being lost.

If I pump it up to 80 PSI, the button won't depress. Even pushing down the pin in the middle of the Schrader valve won't release any air. If I undo the bottle's lid a bit and let some air out, the AirZound behaves as described in the paragraph above.

Does anyone recognise these symptoms, and have a solution for them?

I've tried taking the diaphragm out and running water through. There didn't seem to be any sign of an obstruction and when I put it back together the horn appeared to work. 24 hours later it was dead again, insofar as I was back to the symptoms described above in the "pump it up to 80" paragraph.