Thanks for putting up that video. You've got some action/neck relief issues going on. You shouldn't get buzzing like that. Check the relief (Google to find out how). Your neck might be too straight or too concave.

If it's too concave you may just have to tighten the truss rod just a tiny bit and/or adjust the bridge saddle height. If it's too straight then loosen it a tiny bit and see what happens.

My guess is since you put on the heavier strings you have a little more bow in the neck, so a little tightening of the truss rod should help.