The dealership has had my 2016 for 8 business days for no AC. Mine “thumped” just like yours. Leak tests and AC system pressure test were negative. A corporate tech informed me the front and/or rear evaporators are a known problem, more commonly the front. The dealership is now tearing apart the interior of the rear of my vehicle to get at the rear evaporator. My dealership STILL doesn’t have a diagnosis, but I subverted them, reaching out to Corporate to get some insight. Hope this helps!