The Law & Order sound is the strangely reverbed clanking thingy that accompanies black title screens on episodes of Law & Order and Law & Order: Special Victims Unit that indicate a sudden scene change. E.g.:
4132 Some Place in New York
[Time — optional]
*Law & Order Sound*
According to IMDB, the noise was created by mashing together about a dozen different sounds, one of which featured a bunch of monks stamping on a floor. This is by far the most interesting fact about the sound, but of course, since it's IMDB, you're never going to find even slightly more explanation than that. For years, fans online referred to the sound as the chung-chung, until the USA network started running promos featuring some of the cast. In them, Dann Florek, who plays Captain Donald Cragen (appearing in the first three seasons of the original show and in every season of SVU), referred to the sound as the doink-doink, and the name's pretty much stuck.
Law & Order is on nearly 24 hours per day, and while it isn't the greatest show by any means, it usually can be relied upon to not suck. Thus it worms its way into fans' lives: the show that's always running as a marathon somewhere, sometime, the show that can always be put on in the background while you iron some clothes, dust, make dinner, tinker with something. In this way, you wind up hearing a lot of doink-doinks. I couldn't sleep one night because my mind simply wouldn't shut down, and I found myself watching — you guessed it — Law & Order reruns because every other option involved trying to sell me something extremely absorbent or a twiggish blonde woman walking through a world filmed in blue and seeing dead people and then putting them to rest by asking inane questions of living people who she'd meet and then magically see them as their past selves. So I started to wonder, how many times have I heard that doink noise during my life?
