That's an interesting one. And yes, Sonic support has historical line performance information, and can see graphs of key metrics like signal to noise ratio. We also have an intelligent agent tool that helps us find ground faults, AM interference, bridged taps, etc.
Regarding issues in the heat, I do wonder if there's an AC system at the home that's got an old motor. Sometimes we see local interference from poorly shielded motors causing AC induction interference. Just a guess!
Do give support a ring (or text, or click to have them call you, etc), at https://www.sonic.com/support