Distortion on the Power Line


I have a couple of PS Audio Power Plants.
The distortion off the wall has typically been 3.5 to  4.0.  For the last week it has been over 7%.  I checked around the house and can see no changes.  Anyone have any ideas what it is?  Have Russian Hackers moved in next door?  People huddling at home on their computers?

sm2727
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Commercial air conditioning systems with variable speed motors are the most likely culprits.  They share the harmonic distortion with all their power grid neighbors.