If you zoom in real close on the waveform of your clips, do you find that your tails on either end are at 0 (in the center of the waveform), or are they somewhere else? Having your waveform at either end of your samples not on 0 will cause clicking sounds. The solution, if that is the case, is to load them into your wave editor and put a very short volume fade wherever you have this… the fade does not have to be very long at all, it can be milliseconds, but you need to make sure that your sample clips start and end with the waveform on 0.
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