I have a Goodman furnace in an 850 sq ft house that is practically brand new. When the furnace kicks on it sounds like it is going to start blowing hot air, then the furnace quiets, then starts up again. After about five minutes of running a loud whistle is coming from the unit. It sounds like it is around the flue gas pipe exiting out the roof. The furnace kicks off before the temperature I set is reached. Please help, I really don't have the money to have someone come out to look at it. Thanks, Chris

Check your filter and check for air leaks