First of all...welcome to the site.
Before you call in guostbusters, you may want to look into getting and energy audit done on your house. Your local utility company should have any information to help you out.
Most cost about 50 to 100 bucks, and the companies will do a blower door test on your home to find where you are losing the most heat...that's one reason for the howling you heard, the heat goin out the window from suction. I'm guessin you have either vynil siding or storm windows on the outside? They are notorious for howlin,also. Energy companies will also change your lightbulbs, check your heating and hot water, and weatherstrip your doors and windows, sometimes for an extra fee. But you can decline and do it yourself, however you will not have the blower door to test what you did afterwards.
My opinion, go with an energy audit, call for references of past customers to see what happened on their homes. And I can guarantee it will save you $$ in the long run.
Tell us how you make out, and good luck.