Escort weird air behavior: Please help!

Hi :(
Brief summary: 98 Escort SW, just had engine replaced recently. When I turn on the cabin air controls, there is a periodic hissing/scraping noise (about 5 seconds on/5 seconds off) in all positions EXCEPT the
"blow air from face-level vents" position. It sounds like a motor, valve or compressor is cycling off and on. In fact, it sounds like the A/C compressor is cycling. Feels like it is loading the engine down too.
Any ideas what this could be? Again: It doesn't happen when the air switch is in the off or "arrow-pointed-at-face" position one step CCW from off. But it does happen in all positions CW from off, and in both A/C positions. In the A/C positions, the "on-time" of this noise is longer.
Problem doesn't seem to happen when the engine is stone cold.
Would really love some suggestions here.

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