I must have a site out there running my code that I do not know about. I am receiving about 500 imps a day from an unknown site. How do I find out what site it is?
If you have a lot of traffic, it could be from views of your cache. I had more clicks in aggregate than by channel, so I emailed G about it. They said if someone clicks an ad while viewing a cache of your site, it does pay you, but doesn't go into the channel for some reason.
I had a similar problem, but it transpired one of my earliest sites had code without a channel - it may be worth double checking its not the same for you.
make sure everything is channeled, if really that much of your income is from an unknown site, you should contact adsense as most likely someone is using your code
I've found more an more people are using the google cache of a page rather than visiting the page itself.