midi noise at M-audio Fast Track Pro headphone jack but not at midi keyboard's jack

Keyboard- to -M-audio Fast Track Pro- to -DAW For some patches there is crackling/popping noise at the M-audio headphone jack; but, not the keyboards head phone jack. For instance the noise gets generated when playing the harp but not the grand piano. This noise shows up in my DAW. And in another hardware configuration it shows up in my Komplete workstation. Does anybody have any ideas how to solve this?
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