What is keeep?

Onamatopeioa of the sound a step-on switch makes in Sonic The Hedgehog for Sega Genesis. Consists of a 3507 hertz square wave for 35 thousandths of a second. Sound Test on Sonic 1 is number "CD". A silly noise to make when you switch on a large/powerful appliance (microwave ovens actually make a similar, though not identical, sound) or flush a toilet.