This seems the be the culprit! Wow. Thanks so much.
It seems like Armbian is using ondemand and the official image is performance. As soon as I set the governor to performance, the noise is gone. Once I set the governor to ondemand, the noise is back. This occurs on both images. I've not tested pinning the CPU frequency as it was just a quick test. I noted that CPU frequency is pinned to 1.5Ghz and 2Ghz on performance while the ondemand governor puts the little processor to 600Mhz. This is probably the reason for the noise?
One thing that I find strange, I noticed that armbian's boot.ini, there's the line setenv governor "performance". However, this seems to be overwritten by /etc/default/cpufrequtils.