Newbie getting shrieky sound

[graphicsgeezer]

Just bought my DR-05 recorder and tried it in a church basement where a choir was singing. Got some rather shrieky sound with high pitch 'burbling' noises which you can hear here: https://www.dropbox.com/s/wtaj0rvmwsdh2wf/choir.mov?dl=0

This is my first attempt to use this recorder so it's probably my fault, but I've been thru the manual and can't see where I might have gone wrong.

Any help appreciated.