Windows 7 - Clipboard Automatically Pasting

I have a strange issue happening on my Windows 7 x64 system. For some reason, the system is automatically pasting random characters on a constant basis. It's weird. I can walk away from the computer and be completely away from my keyboard, and every few minutes the system automatically pastes a set of random characters wherever the cursor happens to be positioned. My first thought is that I must have some sort of malicious bug. I ran MalwareBytes Antimalware and it came back clean. I also ran Spybot Search & Destroy, and it came back clean too.

Any ideas what could be causing this? It's strange. I couldn't find anything through Google, and I'm stumped.

My compliments on running the scans, which would be my first advice.

Do a clean boot and see if it happens.
http://support.microsoft.com/kb/929135

If the problem persists, try in safe mode. These steps will help us determine the cause.

I rebooted, and the problem is still there. It must be some sort of malicious junk. Maybe there's a better scanner?

See my post above

Good advice. I'm going to reboot in safe mode and rerun the scans. I'll also run my ESET scan and will post back later this evening. Thanks for the help.

I would have a look in Task Scheduler under "Active Tasks" and check the triggers. Maybe you can identify a culprit. Task Scheduler is in All Programs > Accessories > System Tools

I will be waiting and hoping for the best.

Thank you to everyone for the tips and advice. I rebooted into safe mode and re-ran the scans using ESET and MalwareBytes AntiMalware. They both came back clean. I did a normal boot, and the problem is still there. I run a complete system backup every couple of weeks, and I keep a history of several versions. I'm just going to restore a recent version overnight, so everything should be clean in the morning. It's just an easy resolution, and I won't have to spend days trying to find this needle in a haystack.

Thanks again for all of the help.

If it does not work, we will be here for you.

Well, I reinstalled a saved system image that was about a month old. I'm positive it was clean, and I was not experiencing this problem at the time that image was created. As soon as I reinstalled the image, I noticed that the problem was still there. Now I'm really stumped.

I was thinking about the issue and thought that perhaps it was related to my keyboard since there are characters mysteriously pasting about every 30-60 seconds. I uninstalled my keyboard driver (Logitech), and unplugged it from my computer. Before doing that I opened an empty notepad file. Even with the keyboard uninstalled and unplugged the pasting of random characters continued.

I'm very frustrated at this point, and I'm hoping someone can help me. I've never seen anything like this.