Red-breasted Nuthatch (Sitta canadensis) song, September 5, 2009, Emma Carlin Trail, South Kettle Morraine, Waukesha, WI.
This appears to be the “agonistic song” as described in Birds of North America Online
Earbirding.com (great blog on bird sounds) has a very informative article about nasality in bird sounds that uses the Red-breasted Nuthatch song as the classic example.