Behind our house is an old 2 story house that is used for storage. Probably built around 1900. Well last night hubby was n the back porch of it moving something and the wall by along the porch started humming. Yikes. Haven't noticed anything flying around in yard or in garden or flowers. I mow by it every week. Guessing it may be bees. But haven't noticed any. Leaving it alone until it gets cold or we have a problem. Any ideas besides bees. The wall is hollow. Just wood siding on outside and wood on inside.