Last year on one of my bird surveys, I head the craziest sparrow, it sounded like a really groggy field sparrow and I wondered if it was a hybrid clay-colored/field sparrow (something has been documented before). Here's what it sounds like: http://youtu.be/Mdl8zHt6CaY
I tried like crazy to get a photo of the bird last year but wasn't able to. I was only able to get video of it singing. On Monday I was in the same area and I heard it again on the same survey site. Alas, I've never been able to get a good view of the singing bird it's now on property that I'm not authorized to walk on for surveys and this vexing singer may have to remain one of Life's Great Mysteries.