Well, I have also had a lot of problems with the low end whistles in D being in tune. Metal whistles go flat if they are cold and must be properly warm. You can find good low cost whistle that are in tune, but it is a case of having to kiss alot of frogs before..... You may want to consider investing in a high end whistle. If you buy a whistle FROM the maker it generally will have a guaranty. I yet to find a good (in tune either to pitch or to itself) generation,oak, or feadog although I know people who have them and they are fine. I have a nontunable Silkstone composite, a Brass burke, a harper, and a copeland that are all wonderful whistles and in good tune. I also have Shaws, which are very affordable, but require LOT of blow, that are perfectly lovely sounding and in quite good tune. Check on Chiff and Fipple. Many of my whistles were purchased from people on the board. One of my favorites a copper Parker was bought second hand for about half the money of new, AND Mr. Parker extended his guarantee to me, the second owner. You can buy a bunch of lower priced whistles till y ou find a goodie, or just spend the same amount and save you time and aggravation and get a lovely hand made whistle.