Sounds like you have noise on the line NOT coming from the air conditioning.
Cellphone chargers are notorious for this.
Tell us more about your setup.http://www.smallnetbuilder.com/
PS: A powerline surge could theoretically have damaged one or both of your units. Also I don't know how they work for signal filtration, if any... as a comparison, the little DSL filters you have to install between a DSL enabled phone line and any POTS equipment installed... those wear out. When they wear out you start getting real connectivity issues with the DSL end for some reason. Which is weird, because you would think that the only result would be that you start hearing noise on the POTS equipment due to the filter being blown...but no, the DSL equipment will start having issues as WELL as having noise on your phone.