Something that comes up from time to time in threads is someone who has acquired a high-end whistle but not directly from the maker, and are now having difficulty playing it.
A couple of thoughts I think are worth sharing on this.
If you have a local session or know local musicians, see if a whistle player will check the whistle for you and confirm that it actually does play ok.
If you don’t, then you might want to give serious consideration to sending the whistle to its maker for a check-over. Most of the makers will actually be grateful; they don’t want whistles bearing their name floating around that don’t play well, for obvious reasons.
Nobody except the maker of a high-end whistle can really fix a problem if there is one.
–James