It sounds as though, on occasion, the supply voltage to your house is too high. There is one circumstance where this can happen without any obvious reason or showing uo on your neighbours' supplies. It's not common and a bit complicated to explain, but here goes:
You're aware, I'm sure, that the supply from your local substation is 3-phase, ie 3 separate supplies at 120º to each other, with (usually) houses connected in sequence, so that every third house is connected to the same phase.
These 3 supplies all use a common neutral connection which is earthed at the substation. If this connection should develop a higher resistance than it should have, it won't do any harm provided each phase is taking about the same current
, all that will happen is that the voltage on all 3 pheses will drop a bit more than normal.
Note that on a perfectly balanced system the current through this earth connection is zero, so the value of the resistance can get (comparatively) high without showing up.
If, however, the phases are taking different currents then the behaviour is somewhat counter-intuitive- the voltage on the phases taking higher currents will fall (as expected) but the voltage on the other one may rise
, by an amount depending on the value of the resistance and the degree of load imbalance. If the resistance and/or the load imbalance is high then the rise can be substantial. (This happened to me once at work- the office lights seemed brighter than they should be; when I checked the mains voltage it was about 280v!)
There's nothing you, yourself, can do about it- all I can suggest is that you contact your local leccy provider and explain what's happening, quoting the above if you want to. They can check the earth-neutral integrity at the substation and/or put a recording voltmeter on your supply to see what's going on.
If I come up with any other bright ideas I'll post again- good luck!
Edited by billford (Sun 10-Jul-16 23:04:42)