Hi, I have a Chevy Impala 3.8 v6 . I have only had the car since thanksgiving and haven't had any problems with it until this past week. I noticed when I was sitting in the car when the cars running the temperature gauge would move to the middle and would seem as thought it was over heating but as soon as you drive it goes all the way back down. I checked the coolent which was fine and the oil level is fine . Yesterday it started making a knocking noise and the car vibrated a little but it goes away after you have been driving awhile. Does anyone know what this could be I know it's due for an oil change but I'm scared it's something seriouse it's wierd how it starts the noise and then goes away . I would take it to the repair shop but there isn't one where I live that I trust . Thank you in advance for any advice .