What version of Hazel are you running now and do you recall ever running an older version (like the 1.x series)?
If you look in your Library/LaunchAgents folder, do you see any files starting with "com.noodlesoft"? If so, I would remove those and then logout and back in.
Also, double-check your Login Items. You can view them in the Accounts->Login Items pane of System Preferences. HazelHelper should be the only Hazel related thing in there.
Let me know what you find.