Emptying Thoughts

How can I ever accomplish anything when I'm so busy carrying on conversations in my head? I'm not hearing voices, so you can put down the phone, there's no need to send someone over to check on me. There's a voice, one single voice, in my head that just won't shut the hell up. She, me, I won't stop talking, asking questions, addressing issues, concerns. I've been told by people "you think too much" and I believe them but is it possible not to? How does one clear one's mind? I thought motorcycling would be the fix. Countless hours on the road can ease the pressure but I can still hear the voice inside my helmet. What can I do to ease the pressure, get answers to the questions, sweep out the cobwebs and use the remaining brain cells for something productive?