AD Account lockout issue:-
To find out the bad password attempts and sources from below tools.

http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=18465
http://www.netwrix.com/requeste.html?product=ale

After getting the source machine check if your account is using old credentials for any following task on source machine.

1-            Mapped network drives
2-            Scheduled tasks
3-            Accounts that are used for service account logons
4-            Run as shortcuts