Wow! What a great response! I didn't realize I had a response till I drilled down into my message. I was about to delete it.
So it is NOT tied into the septic. We live in an area that is all septics and even a few cesspools I think (Outer Cape Cod).
There is no smell.
I've been here almost 13 years and just ignored it. So I put a stick down the hole and realized it's solid just a few inches down, so it was either filled in or just became that way over time.
Thanks again for all the helpful advice.
Rod