Same thing happening to my R65 although worse in ryegrass and clover, replaced side seals on fan deducting (need to remove shoe to do this) and silicone around fan deduct and frame, even screwed draft stopper door brushes to top of wooded shoe seals, helped a bit. All other seals appear ok. Possible grain is being flicked up by thicker flighing section on clean grain elevator and catching air flow. Is there a solution as looked at it many times?