Mysterious Bird Call in Michigan?

I am sitting in my backyard and I was wondering what kind of bird this is. It is always sounding off, all day, and is still sounding off at 7:00 pm. It is in Michigan... lower Michigan. It sounds like Chee-Chee-che,che,che,che,che,che. The Chee-Chee is lower than the che,che,che part. The che,che's are very fast and there is always 6 of them. So a step down Chee-Chee then a step up, chechechechecheche. I know people are not going to be able to answer this, but if you can, you are my hero cuz its been bugging me. All I need is the bird name.