Make sure you indeed hit the reed with the tip of the toungue, not the fat part. Practice doing this over and over until no percussive sound is being made. My teacher tells me to stand in a corner and hear what sound i make. I have similar problems specially with some areas at Le Cabridan from the Tableaux. Quick strokes with the tip of the toungue is what you need to get to. I would recommend doing scales and toungue the notes correctly at a slow tempo. The secret to being fast at anything is doing things at a tempo marking of 60 for hours at times. Also reeds do contribute some effect to your tounging, make sure its soaked and warmed up for proper execution. Hope this helps