Scrunches are dissonances in diatonic music, caused - usually - by having different musical lines move close-together: either in counterpoint, or progressions of harmony when the parts have some autonomy.
Generally they are transitions - in which what will eventually be a consonant note comes a bit early, or where a peculiar transitional note is used, or when a note is suspended from a previous harmony; at any rate scrunches are en route to resolution and relaxation on a major chord.
I love them.
They usually come in Renaissance and Baroque music.
Like this Crucifixus by Antonio Caldara (c1670 – 1736):
Tell me, please, anybody - why this sublime piece of music is not world famous?
There isn't anything better than this. Different in genre and equally good, yes, but this is perfection of its kind.
As is O Nata Lux by Thomas Tallis (c1505-1585)
The scrunches near the end are an exquisite agony.
Note: wrt Caladara Crucifixus: This version is slower and it is easier to hear what is going-on in the counterpoint - tho' overall I find it less musical, somehow: http://www.youtube.com/watch?v=8WPkfGd1q-s . This version is an amateur camcorder recording, but extremely good: http://www.youtube.com/watch?v=QK-bPccxLME