Humming Noise Reported in Calumet, MI

I’ve been hearing an industrial humming sound for awhile now. It sounds like it’s coming from under the ground. The sound varies from not very loud to louder. It’s on going and the sound rarely stops or maybe it just becomes more quiet? It’s a steady hum, like a vacuum was turned on but isn’t being used.
There are many old copper mines that shut down years ago. Just wondered about that. I can hear it in the house and outside the house but don’t notice it when I’m away from the property.

The question asked below, is when did this happen? I don’t remember exactly when I first started to hear it. First time I heard it I looked at my husband, shocked and asked if he could hear that? He said no. The date is estimated but it’s been at least a year or more.