2015 S 85D with around 21,000 kms. Noticed a slightly annoying noise coming at around 110 to 115 kms/hr (around 68 - 72 mph), only when accelerator slightly pressed, so under a light load. It's almost as if a rear window was slightly open, but it's not anything wind - as soon as I step on or release the accelerator, the sound goes away. It also doesn't happen at other speeds. It's like a deep rumbling noise. It's not the typical milling noise that I've been reading about. Service center says they can barely hear it, but will keep a lookout for any tech posts about it as they don't know what might be causing it. Anyone else experience something like this?