Mine is NOT the seat AC. It is the general AC. Also when I am in park the noise subsides - it is only when I am moving that it happens every 8-15 seconds.
I purchased a GX 550 Overtrail+ in the last couple days and immediately noticed the same "hissing" as everyone else. Has anyone been able to get a straight answer from Lexus? Do the Luxury or Premium trims also have this issue?