Very Annoying Squeak From Heater Box

[dually2002]

My 02 has a very pronounced and annoying squeak coming from the heater box when I am running the A/C. More apparent at moderate temps than hot. Almost non existent when not using A/C. Is there anything I can zero in on when I bust it open to trouble shoot?

[DmaxMaverick]

If you haven't recently, change your cabin air filters (2 of them).