Was this a hard puzzler? I bet if I had mentioned the fact that this animal is nocturnal and a mammal, you may have guessed it. It’s not a bat though!
Those sounds were from a flying squirrel. In the United States we have northern and southern flying squirrels. I have no pictures of this animal! I have seen them a handful of times–mostly from years ago when I was monitoring bluebird boxes. Every once in a while I’d open the box to find a startled flying squirrel. He usually dove out the opening and scurried off out of sight, likely wondering why I was disturbing his peaceful nap. 
Flying squirrels do not really fly as their name suggests. Instead they GLIDE, from a higher place to a lower place. Unlike bats and birds, flying squirrels can not start on the ground and fly up into a tree. They CAN climb the trunk of the tree and then sail back to the ground or to another branch. They have flaps of skin between their front and back legs, like a person wearing a wing suit. 
These squirrels are common but since they are nocturnal, we seldom see them. Has your bird feeder ever been empty in the morning when you could have sworn it was fill the night before? Maybe a flying squirrel has been raiding it!
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