Recirculation Vent Cycles

I have a 2001 GMC Yukon XL. I am not able to switch the air flow between internal (recirculation) and external. When I try it seems that the vent is cycling back and forth between the two. I can hear something in the dash that sounds a bit like bees. Is there some way to disable this before something burns out or better yet is this something I could repair myself?

The problem may be with a detached blend door or a faulty electrical blend door motor.

I had a motor replaced in my '02 Tahoe when I had a similar problem last year.