Two weeks later, the Clarke's D is sounding much better - to begin with. What seems to happen now is that it plays fine for the first couple of tunes, but then most of the lower register disappears: getting anything below G to sound at all is a struggle, and getting a true note without overtones is more or less impossible. This usually happens just after I've blown a bit of spit down it, and a good sharp blow does help a bit - but it doesn't really fix it. Any ideas?