Put your finger over the hole- do you feel air moving? If you don't, it means there is something in their somehow and should be cleaned out with a pipe cleaner.

If you do have air movement, I don't know what to tell you. I've used all of the Fox models and it doesn't take much air moving through them to leave you in pain if you are silly and blow it inside. Don't worry about being gentle, blow on that sucker, and blow it outside. Don't toot it, blow it, like you are blowing out candles on a cake.