According to WMTW, the low flying helicopters in Central Maine are nothing to worry about.  They're part of Royal Canadian Air Force training missions.

A Lewiston PD spokesperson said, "The flying exercise will occur during daylight hours and consist of overflights, landings and takeoffs in order to expose Canadian aircrew to the unique challenges of flying in mountainous environments,"

The flights will be seen around Lewiston / Auburn as far Southwest as the White Mountain National Forest in NH.

The flights will run through March 27th.