Can anyone tell me why a note on a melodeon might sound wheezy and asthmatic (sp) and why it doesn't sound immediately but seems to have an '80-a-day-smoker's' wheeze before it sounds and then sounds weak and nasty?

Is it the reed or the valve (or both!)?

I have had the F sharp in the middle of the D row fixed twice for this fault and it's gone again. It was fixed for me when I first bought the box and complained that the F sharp was wheezy (I was the first owner but it had been in the shop and taken to lots of festivals for a long time before I bought it). The 'fix' wasn't really very good and, before long, it went again. I had it fixed again about 3 months ago but now it's as bad as before.

The box is a Castagnari Matti (3 row / 12 bass) and I know that the middle row is weaker than the others but that's not what I'm talking about. It isn't that the note is quieter but that it's wheezy and nasty - it sounds like a very old box whereas the rest of the box is fine (OK not the D and E in the middle of the D row - they're nearly as bad). Why is it just these notes? If it is the box design that's at fault why isn't is all the notes or even most of them?

Anyone any ideas / suggestions?