Hearing hum near natural gas gauge, should I be concerned – Pic Attached

It is (very) surprising that the gas company (Xcel) says "everything's fine." This document from a different gas company certainly calls out non-blue flames as an issue that needs to be resolved. As does this site. And Xcel themselves.

Happening on all appliances does seem a bit less likely to be "and suddenly the air adjustments on all three went whacky" than a contamination issue - possibly water in the gas line?

I wonder how your furnace tech visit went, and what your neighbor's flames look like.

Editing post-comments: Ultrasonic humidifiers make small water droplets (without evaporating the water first) and then those small droplets evaporate while floating around - if the water contains salts or minerals, any salts or minerals in the water will end up floating around the house as tiny specks when the water evaporates from the tiny droplets. Those, evidently, are what is contaminating your gas flames as they are sucked in along with the air required to burn the gas. Old-style "sponge" dehumdifiers (should) only result in water vapor in the air, as they actually evaporate the water (and this eventually leads to a build-up of scale and salts in the humidifier and its sponge element, as those do not evaporate.)

Your 2# regulator is likely dropping the pressure down to about 1/4 psi which is what most appliances need. By putting the tee after the regulator and running a 80ft line isn't going to be sufficient. Longer runs generally need larger piping. Your 1/2in line wont be able to keep up. You probably should have ran the 2psi line (i.e. a tee before the regulator) and installed a 2nd regulator up there.

Here in the United States, most houses are fed 1/4psi after the meter and if there is problems with piping or a need for large appliances, generally pressure can be increased to 2PSI. Since you have 1/2" gas piping, that might explain why you have 2 PSI of gas. On my house, the line coming in is 1-1/4".