Pretty common problem in kids we teach to DL that have done primarily cleans at sports practices..
Two things. You need to think of your arms as hooks and relax them. Also, before you pull contract your lats. My observation has been the motion you are describing actually originates in the upper back because your body has learned a pattern of motion that makes it want to prepare for the clean.
If your lats are contracted (pull shoulder blades down and lock it in like this) you really can't bend the arms. You should be doing this anyway b/c it will shorten your stroke and go a long way towards tightening your upper body.