The first Gray I heard this year was about 3 weeks ago. A week and a half ago we had a big rain and I heard tons of Grays calling, and found a couple who were sitting quietly. April was unseasonably warm here (southern Ontario) and dry though.
For me, Peepers are easiest when they are so abundant that you nearly step on them, or are scarce enough that you can single out a calling one to home in on. Too many calling Peepers and it's just a loud blur and I have trouble locating anything. I have a slow moving stream with lots of small temporary pools around it right by my house, and the calling peepers are very spread out and no problems to locate in the evening. I've never trapped one though.