My GLC 63s 4matic has developed a clicking noise, it seems to be coming from the transmission tunnel near the rear air vent/arm rest area. At first I thought it was coming from the front passenger foot well area because the way the sound bounces under the car but I am now sure it's from the trans tunnel. Strange thing is it will only make the noise when the car is cold and goes away after about 1 mile of driving and it only does it when I let off the gas paddle, clicking noise goes away when I accelerate. Once the car is warm the sound goes away until the next day on the cold start.

On the video you can hear the clicking sound when I let off the gas and in person it sounds alot like a straw stuck in the wheel spoke as it turns and less of what the video sounds.

Here is what is happening so far.
1. Clicking sound when decelerating, goes away when accelerating.
2. Only on cold start, sound goes away after about 1 mile of driving.
3. Sound seems to be coming from transmission tunnel area under rear air vent/arm rest area.

Any ideas on what could be going bad?