I have six hives at one location. One two deep hive has been making a buzzing sound several times this winter when the other hives are completely silent. I thought something must be bothering them, like a mouse or something, but when I got into the hive on Feb. 1, all I found was dead bees on top of the inner cover. I cleaned them off and replaced everything. I have since gotten into them two more times and found the exact same thing. The second time I took them down to a single hive body. I was wondering if I have a moisture problem and the bees are trying to fan the hive through the hole in the inner cover. The inner cover and the lid are plastic. This hive also wants to make more propolis than the other hives. Any thoughts on what could be wrong. Thanks.