It is, according to an amusing contribution to Lugnet the sound made when digging through Lego to find a particular piece.

Pronounced - “Groo - shtell - ing” - it can be used as a word for searching for that one little piece you know is there but you just cant reach, like a 2x1 or a technic pin.

More seriously - if you are using a great deal of Lego for building robots (with a Lego RCX) or other inventions - then you should probably seriously consider some more convenient Storage Systems. Not only will it spare your (relatives) ears, but it will save you a great deal of time.

One other method I have seen of avoiding this is to tip the whole lot onto the floor before starting- but then you only have to put them all back again - and you stand a good chance of loosing or damaging pieces. Some people use a big circle of cloth with a tie - opening up the circle and spreading the Lego on it, then closing it up with the Lego inside when finished.

Either way- if you are going beyond the basics- then keeping it all in one big bucket/case is not a very good plan.