They do that every night at my house in L.A. For years now.
Living near the Forest Lawn neighbourhood of Calgary, the local cops have also been daily flying over my neighboorhood for years; no loudspeakers blaring so far, though. A city of 1.1 million, with two police helicopters, wow!
I lived in L.A. for decades. If I didn't hear helicopters every night, I got the creeps. Just felt like something was 'missing' - you know?
I got the heck out of there 9 years ago and moved to Texas. I hardly ever hear police helicopters anymore, and I like it that way.
Yep they are normal here too. We call them Ghettobirds.