Electric cars will ruin late night listening?

oh brother...

Take an ordinary Lamp.....unscrew the bulb and replace with a screw in socket....plug your Stereo system into the lamp...turn lamp on. This alleviates any such problems.

 felt he now had DC in his line because his tube amp started to get a mechanical hum. 

I assume your repair guy measured DC current in his line versus simply "feeling" he's got issues. Regardless, wouldn't a decent power conditioner resolve this very issue? I thought that's what power conditioners do - eliminate voltage spikes and remove any interference/intermittent frequencies that ride on the main signal. 

I know some don’t agree that there system sounds better at night and I understand that but at my house does sound better late into the night. You would think if cars are charging at night it would affect my power, right?

I agree with music sounding different at night. Reduction of ambient noise caused by vehicles, people, pets, businesses etc. would all factor in... and the hum from appliances like fridges, microwaves, HVACs etc. are significantly reduced at night.

But I don't see that change in sound quality as an attribute of better power coming into my gear at night :)

Why would the hum from appliances and HVAC be reduced at night?

Bugsnest, I don’t think power conditioners help DC in your lines, they may but it didn’t help me.
 

I have a Running Springs Dmitri, Hayley and PI Audio Uberbuss and tried them all when I had a mechanical transformer hum on a Conrad Johnson amp. I had to send amp in for a replacement in 30 day period. The new amp had no hum so my problem may not have been DC in my line.

If you have DC in your line you can try a Van Alstine Humdinger DC line blocker $140. That was next move if new amp still had hum.