If it's a powerful airborne frequency or magnetic field i would be more worried about what it's doing to me, there would be strict interference rules against these things, there are in the UK, so i doubt it's that, more likely an issue with your wiring and voltage.
If this is an apartment i would first ask other people in the building if they are experiencing the same thing, especially the people directly above or below you, there are power conditioners, i use one for my home cinema room, more to protect against surges than condition the line but here is a link, you can find others on Amazon by putting power conditioner into the search bar, i do not know how well the one linked to works so search out some reviews from external sites before you purchase anything.
In fact you will probably find all they do is filter out the clicks from your fridge door and lights being switched on, as well as old lawnmower noise, that all used to drive me mad but they cure that, you can also buy voltage conditioners, more likely to solve your issue than the above and remember Amazon has a 30 day return period, try and if they work then good.
The above will only lower voltage that is too high by 6%, there may be other brands out there that do better, not convinced though that the power would be excessively high in your apartment and if it is then a 6% drop is not going to really do much, your power is probably within tolerance levels or they would have fixed it, you need to find out what they meant when they said it's a bit high, is it 10% over, 15% over, 20% over, a figure would be needed.
I would really ask others around you what they experience first and carefully test your equipment, plug it into every socket in your house and note the results, you say during storms there is a small improvement, signals can degrade during storms so if something external is causing interference it could be weaker during a storm, for distortion and external i would think magnetic.
Bit confused though, in a post above you talk about an RCA 32 inch television and say the stretching is not on that set, i would be questioning things then, why is it on your other sets but not that one, that would surely rule out voltage and interference and point to issues with the other sets instead.
As Sherlock Holmes once said, once you have eliminated the impossible, whatever remains, however improbable, must be the truth.