Thumping noise in heater box...valve or flap not opening?

[J Petty]

Anyone know anything about what could make a thumping noise coming from the heater box area under the dash of a 93 Yukon?

 

[gpracer1]

Most likely the recirc door actuator has a broken plastic gear inside it.

Been there, done that on both my 93 and 99.

 

[J Petty]

Is it hard to fix and where do I find a replacement part for it?

 

[WiCK3D_SiX]

Typically the thump comes from an actuator.