Did you know that your outlets don’t last forever? We had to replace all our outlets after 30 years because in 1981 the popular outlet had a compression fit for the copper wires instead of the more conventional screw connections. Over time these older outlets can give you problems with loose wires and bad connections. Simply installing new outlets with screw connections has resolved our problem. However, I plan to look for a Suretest circuit analyzer to double check all the grounds in the house.  You can get some pretty clear instructions on how to replace the outlets yourself via searching youtube.