The book is a series i believe and it involves a whistle of some kind, there’s also sand involved? I feel like there might be sand and whistle in the title even. It’s magical I believe, happening either in the desert or in a made up place – I vaguely remember a scene of MC getting to a town/village square and having to climb somewhere to blow the whistle? That could be very wrong and I misremembered it. It involves fighting and such, probably YA considering it was in our school’s library. It’s definitely a series and the books have different titles, this is just the one i remember mostly.
Lost Classics of Teen Lit: Name That Book! 