I took this picture of this hawk in my yard last week. I live in Western Pennsylvania. For size reference, he’s sitting on a 2x4 so that the side of the board that you can see is 3.75 inches tall. When the picture was taken he was eyeing up a chipmunk in my neighbor’s yard which he soon flew over and ate.
I’ll go with juvenile Cooper’s Hawk, but I lost this argument last time :D. The other possibility, as always, is a juvenile Sharp-Shinned Hawk.
Juvenile accipiters are always kind of a bitch to ID.
- Tamerlane
According to Whatbird.com, you may choose from among these.
It’s a Cooper’s.
This time I agree with you. 
The big blocky head and rounded tail in particular say Cooper’s to me.
That’s a great site which I did not find googling. Thanks for the replies, I would concur with juvenile Cooper’s Hawk based on those pictures and the sound of the call which I did hear though I of course know nothing about birds of prey or I wouldn’t have asked in the first place.