[Uncletg]

I have a 2004 T/C and the check engine light just came on (solid not flashing). The service manual says that if not flashing it is ok to drive, however, I can hear what sounds similar to a pump or servo frozen (light hum). There is no noticable driving differences. The sound that I hear can be heard "winding down" when I shut the vehicle off. This noise could have been there for ever and I just haven't heard it because I haven't had a reason to listened for a problem. Gas cap is not damaged. It just started raining here in Az., could it be a wet emission sensor? Any ideas will be appreciated.