No ice NO thunderstorms ( rare) NO humidity temps rarely day time even in winter below 50  and on the peninsula rarely over 85.. 

I think we are having this issue because of the high humidity lately.

I live in a "high-desert" area where the humidity is low and the evenings cool off nicely.

To prevent this, keep the humidity levels low.

There is no visible signs of mold inside and the humidity is at an ideal level (30-40%). 

I use a smart thermostat to let me know when the temperatures and humidity are out of range and it uses ifttt to notify me.

Or if humidity or frost are occurring.

Yes approaching triple digit temperatures and triple digit humidity is brutal!

We are a very wet humid state that can wreak havoc on wood framed properties (wood rot, termites, storm damage).

We have also seen the same in venting when the a/c is run very cold & you have serious condensation (from in-house high ambient humidity) laying in the venting laterals & it also has a distinctive odor.