Hi New Daddy,
Do you have information on where you heard that sound? Specifically, was it near/in a pond or small lake? Was it up high in a tree, or down near the ground? Your recording seems to be dated March 22 -- is that in fact the date?
I ask because I and another BirdForum member, dhavlena (who posted something back in June 2010), have heard a bird in the treetops that sounds very similar to a Spring Peeper. I listened to your recording, and it sounds pretty similar (though a little faster and with more variation in pitch) to what dhavlena posted and I've heard. I also note that your recording is of a single individual, while in my experiene, Spring Peepers usually peep in a large chorus. The only time I hear only one peeping alone is when the temperature is a bit chilly for all but one extra-hardy frog, and that'll happen for just a few hours on one night. So you may have heard the same bird. (Spring Peepers ARE extremely loud, though. In my backyard I can hear them from a pond that's about 400 yards away.)
What dhavlena and I have heard is a bird that calls from high in a tree at night for hours on end, and sometimes hops from tree to tree. It's quite loud, and can be heard through closed windows. I've heard it calling from September to April, and as late as 2:00AM and 4:00AM. It's always a single individual.
Dhavlena said he also saw it hopping from tree to tree, and it was definitely a bird. But he only saw a blur as it flew, and never got a good look. (I've never seen it, but I'm going to try to spot one this fall.)
What I've heard is definitely NOT a Spring Peeper, because the Spring Peepers around here (Connecticut) *only* call in the spring (early March to late May), definitely not in September, and (from what I've heard anyway), they call from low brushy areas at or near the sides of ponds or small lakes, not up in the trees. Spring Peepers also tend to quit their peeping around midnight to 1:00AM, while I've heard the treetop peeper until just about dawn. And I think the treetop peeper's sound is a little different, slightly more drawn out, and plaintive.
The best bet for an ID I've seen so far is the Swainson's Thrush, which makes a *somewhat* similar call while flying overhead at night during its migrations. And several people I've seen online have described the Swainson's as "sounding like a Spring Peeper." But I've listened to several Swainson's Thrush flight-call recordings, and I think it's a bit different: softer, breathier, thinner and sometimes more of a "wep" than a "peep." And the Swainson's reportedly fly in huge flocks, so that you can hear hundreds of them peeping overhead all night long. What I've (and it sounds like you've) heard is a single bird that stays in one general area, at most hopping from tree to tree. Perhaps what I and perhaps you have heard is a louder variation of the flight call, when the thrush is resting in a treetop before continuing the migration?
I'm not sure about that Swainson's Thrush ID. And I'm not sure if what you've heard is the same bird; it may indeed be a Spring Peeper. That's why I asked my questions above. March 22 (the apparent date of your recording) is prime time for Spring Peepers, and we had a chilly spring in the Northeast this year, so it may well be that you heard one of those extra-hardy Spring Peepers out on his ownsome on a chilly night.