I just bought this retired 2008 Dodge Charger Police car. It has the 3.5 liter V6 in it. It mainly does it when it is cold and it is warming up. I am just curious though why the engine makes a howling sound. It doesn't do it when I accelerate. Just when it idles.

 

Check your idler pulley. Hard to do a diagnosis without actually hearing it, but when the idler pulley starts to go, it will howl, and more audible during idling.

 

Thank you that helps a lot.