Creaking noise from the HVAC unit?

[Quadraphonic]

Last 2-3 weeks I've been hearing this weird noise coming from the HVAC control unit. It's a creeking noise that occurs everytime I make a substantial change in the throttle pressure. I can only assume the difference in Intake Vacuum Level is causing some problems with the Heater Vacuum Control Unit (I don't know what they're called) which in turn is creeking...?

I hope I'm making some sort of sense. It sort of difficult to explain. It doesn't seem to have any other effect on anything else, yet. The A/C works fine and keeps the passenger comparment nice and cool.

I don't know if they will make any difference, but:
The A/C fan speed does go to low (from high) when I'm on the throttle accelerating quickly. I bypassed the Heater Hoses when I discovered a leak at the plastic ends of the heater core. The engine tends to run hotter after 1 hour of driving, or under load. (3/4 of the gauge)

[Matt95GT]

Makes perfect sense... you have a vacuum line leak to the HVAC controls. The leak isn't noticeable when idle or low throttle, but vacuum is lost at higher throttle and the duct flaps fall open - making the creaking noise. The fan seeming to go lower is actually air being redirected to floor and defroster ducts, reducing the flow coming from main vents. I had this exact issue when my line was leaking.

The "accessory" vacuum line run from the vacuum accumulator (black egg under battery area) along the drivers side edge of the hood. My leak was near the bend in the corner near the battery.

Originally posted by Quadraphonic
I bypassed the Heater Hoses when I discovered a leak at the plastic ends of the heater core. The engine tends to run hotter after 1 hour of driving, or under load. (3/4 of the gauge)[/list]

These issues should be unrelated to the HVAC vacuum operation.