Heater problem

[DJLFourtwenty]

I have a 1992 Cavalier Z24 and the heat comes out hot but it barely comes out of the vents. I cleaned the leaves that got sucked in by the blower motor. The defroster now puts out more air on the passenger side than the drivers side. When I switch the vent selector (far left to far right) I hear the vacuum pressure but there is a now a knock that happens only after the initial switch. The knock isnt very loud but is coming from behind the glove box. I replaced the heater core last summer. Winter is coming and I would appreciate any help or suggestions.