My 2012 Bay Star 2901 has 2 AC units also and the front one (15K w/HP) sounded like a Huey helio was on the roof. A Newmar approved repair facility found the fan/motor was bent and Newmar sent a replacement fan/motor assembly. After it was installed the Huey left and has not returned.
They initially tried loosing the attachment screws, retighting them, and them finally examining the AC's inards.
2012 Bay Star 2901, 2 ACs, 5.5KW Onan, 765W solar & Outback FM-60, 800 AH Lifeline AGMs & Magnum MS2812 + AGS + BMK, Koni FSDs, Safe-T-Plus, Super Steer Rear Track Bar, MCD Duo shades w/powered cockpit, remodeled galley, Sumo springs and 2008 Tacoma 4x4 toad.