Curiously viewing this thread because I want to monitor impending repair issues with mine.

Can't say what's up with the headrest, but the loud ticking sounds like a worn A/C compressor clutch. Noisy when engaged, and probably slipping a bit (since your A/C doesn't get full charge untill your engine is under a load)...

...just my guess.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car