I bought Nexus 6 2 week back. Device got delivered in a day. Surprised to experience poor audio quality during call. Here is my findings in my mobile. I had to return it ASAP.
Poor call audio quality.
Hissing noise( like laptop fan sound) is mixed with audio. Turn on the speaker, noise is clearly audible.
While the hone is idle, just pick up the phone and press the power button, LCD will glow, during this time listen the speaker, noise level increases.
Noise will ON and OFF during the call.
Mobile heats up while charging and playing youtube video for 15 minutes.