I've been playing harmonica for several years now. I've stuck to Hohner Marine Band C harps, but I've owned quite a few. The reeds eventually get sticky, and the notes come out all raspy. Sometimes I pry them apart and gently clean off the gunk, and that fixes it, but other times I can't be bothered and have a gig so I buy another one. I just got a new one as a backup for tour, and noticed that the high notes are choked right out of the box. I seem to remember this happening before. Do harmonicas require break-in? What else could be going on? Note: the humidity here is very high right now. Could that be a factor?