how to remove background noise on recording

I am running audacity 2.0 latest on windows vista. i installed the program from the installer, not the zip. Each time i make a recording there is a constant high-pitched sound on playback. i’ve removed electrical devices, played around with input levels and tried the noise reduction options. as a newbie, i’m at a loss. i’ve attached an small mp3 file so you can hear for yourself.
any help would be appreciated

It’s electrical interference of some sort. If you’re recording on a laptop, try running it on batteries while you record.

OK, so you edited your post - what’s changed?