Lumia 950 :: Makes A Quiet Hiss-pop Noise Every Six Seconds

My Lumia 950 has started making a little hiss and 'pop' noise every six seconds when I'm not using it. I first noticed it last night, because the phone was on a bedside table in a quiet room. Rebooting the phone fixed it at the time, but today I noticed that it was making the noise again. Every six seconds it sounds as if I had gently tapped the plastic body of the Lumia with a fingernail. It's clearly audible in a quiet room when the phone is in my pocket.If I raise the Lumia 950 and put the rear speaker to my ear, I hear about a second of white-noise static followed by a "pop" noise. Hiss-pop. When the phone is unlocked and in use, the speaker makes a contiuous low static hiss. It only hiss-pops when the screen is in standby. Volume levels and disabling glance seem to have no effect. Putting it into airplane mode also has no impact, so I guess it's not likely to be interference from the radios?

If you'd like to hear it, download and extract the attached zip, or download a .wav recording from my OneDrive account, linked below. You may need to put on headphones or turn your volume up, but it should be clearly audible at normal listening levels. You'll hear the noise at 00:01 and 00:07 (the one second and seven second marks). URL>...I love my Lumia 950. But this hiss-pop issue has the potential to dampen my enjoyment a bit if I keep having to reboot the phone to fix this.