Kenmore Progressive Direct Drive Upright - noise and bad suction

Working great, then one day, a horrible sound started coming out of it. When you turn it on, it sounds fine. It's when you put it to work the sound comes out (the tighter the suction gets, like when you put your hand over the opening of the hose, the louder it gets). made sure the bag was ok, nothing blocking the hose or opening. Figured out the sound is coming from this small air filter type opening on the back right behind the hose when it's wrapped up. Loud vibrating sound. If you put something over that small area, sound goes away. Also, the vacuum is hardly picking anything up, which is very frustrating. Any ideas? Very expensive vacuum, only used probably 8 times in 6 months before problem started.