Sounds like you've got birds crashing into the door? That's often something that can be improved (with stickers or hanging decorations) that make the glass more perceptible to the birds. (Another thing that sometimes helps is having bushes or shrubs, or even potted plants, in sight of the feeder - most small birds will use a "staging area" and fly somewhere nearby first, "check out the scene", and then fly to the feeder from there; it doesn't really control the activity, but it adds some options.)