Ant Nickel

trying to find out what kind of insect may be causing this?

We have noticed several (10-12) what look like ant hills in our mulch bed right under our living room window. I have not seen any insects in or around these "hills", so I do not believe they are regular ants. They look just like ant hills except that the opening is a depression into the mulch about the size of a nickel, and there is no hole to speak of. But it has the pile of fine dirt all around the hill, just like an ant hill. The whole thing is about 3-4 inches in diameter. Anyone have any ideas what may be causing this?
I live in Mid-west Ohio. The mulch bed runs between the walkway and our house. It only started about 2 months ago and the mulch is older. We just bought this house in April of this year.
The hills are not against the house, but scattered throughout the mulch bed. There are small bushes in the bed also, and the "hills" are scattered around the bushes.

=years ago I had several cracks in my foundation and noticed the same thing you did. Turned out to be a family of field mice that wintered over in my basement in a bin where I kept rags. The foundation was patched and haven't had a problem since.

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