On my account I am receiving clicks but they are not coming from any of my channels listed, so I do not know what website they are coming from. I have contacted Google about this and they cannot help me. Is there any way to find out what websites your ads are placed on?
If your site has frames in it then this kind of unknown clicks possible because adsense doesn't go well with framed pages and it's not suggested as well. If you have many sites, try "allowed sites" in your adsense control panel where you can specify which sites can show your adsense ads.
Try setting up new URL channels for each one of your sites. That should show you where the clicks are coming from, even if you forgot to put a channel in the ad code when you built the site. (Sorry if you've already set it up that way and still are getting untracked clicks - couldn't quite tell from the OP).
Google told me that it could be a number of reasons, they also mentioned the frame thing mentioned above. But I don't think any of the ads are outside the frame, or anything complicated is going on. Trying the allowed site feature is a risk, because I may forget to include a website and it won't report it anymore, or won't show my ads there. But it's no big deal really, it would just have been nice to be able to know where those clicks are coming from so I could promote them more or whatever. But I'm sure Google has the tools to find out exactly what URL my ads are displaying on too.