Temporary irregularity (4)
I believe the answer is:
blip
'temporary irregularity' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for blip that I've seen before include "Signal on a radar screen" , "Temporary setback - short high-pitched sound" , "Temporary lapse" , "Minor shock or interruption" , "Small mark - unforeseen deviation" .)