in my apartment I noticed recently that my bedside clock and oven clock, which are both powered from the wall, were about 15 minutes ahead. I changed them back to the correct time, but the next day they were already a few minutes ahead. I have also had a few WiFi routers suddenly stop working over the past few months.
Could this indicate that something is wrong with the electricity in my apartment? If so, what can I do to check it myself before calling an electrician?
Update: I contacted the power company and it turns out that the mains frequency was, in fact, higher than normal. There was a water main that burst (and caved in part of the street) in my neighborhood and the city feared that it would damage the underground powerlines, so they turned on the emergency power generators to ensure that nobody would lose power, even temporarily, while they fixed the water pipes. They said that they had to increase the mains frequency in order to prevent damaging the generators. They ran the generators for about a week, but service is back to normal now. My clocks are functioning normally again and it turns out that my router issue was unrelated. Thanks for everyone's input!