I have a 2003 envoy, and not all the time, but every so often I crank my engine, start off and I get a loud roar noise come front my front end, it last about a minute or less then goes away. It only does it when I first start the truck? What could this be? Any help would be great! I've tried to search, but wouldnt even begin to know what kind of problem I need to search for?