Rethinking it might be meredith monk from the LP 'book of days'. you can go to cdnow.com and take a listen to 'eva's song' under the cd 'book of days' if you really need to know. although that one's more of a na-na sound. but thats all there is. na-na-na (sorry, this is getting too weird - just go check it out if it's driving you as crazy as it's now driving me).
i hope you're happy, i'll be up all night!
:)