I too wanted to know who sang this! While looking on the net, I found your entry, making it all that more nagging in my head. You know, it's just playing over and over, driving you to spend hours on the net looking for the answer! So I went on a mission and discovered this great site along the way. With my quest complete, I have returned and registered to the site to give you the answer!
I first thought it sounded like Jose Feliciano. But he never did anything funky like this. Then I remembered that this was a song used in the soundtrack for Any Given Sunday. Found the album online, but the song wasn't on it! Could my vast library of useless knowledge possibly be wrong? Can't be...
I continued to dig. I even contemplated going and getting the DVD. But I finally found it! The song list from the movie of every bit of music used included the bits that didn't get included on the soundtrack. The Internet is a wonderful, powerful thing!!!
So here it is. The singer who also sang "Lean On Me" and "Ain't No Sunshine", Bill Withers with the slow-tempo, growling funky song "Use Me"!!! There's your answer and hopefully you'll go out to enjoy the whole song and stop the cm from driving you nuts!