When the fan is turned on there is a high pitched squeal it changes frequency when i switch from panel to floor or defrost. it sounds like a leaf is hitting the fan blade or something.
There is a high pitched squeal in the heater/ac fan, what might it be? on 2007 Buick Lucerne
That is most likely the case. the blower needs to be droped and cleaned out, normally 3-5 bolts hold the blower assembly in plus the plug and rubber elbow. The blower assembly is normally by the passanger floor bord on the bottom of the dash, however on your vehicle i think it might be in the engine conpartment aginst the firewall. Hope this helps