Even after all these years, YouTube continues to amaze me. Search for it, and you find it almost right away:
Janet Leigh tries to skip town with stolen money, but her boss walks right in front of her car at a red light
And listen to the music, at 0:21!
I did watch this flick again last night (along with the 'Making of' doc, it's great!) and I believe this music snippet occurs three times, in three separate car scenes.
See? A lesson for writers and directors: Just because it's a boring driving scene doesn't mean it can't have an impact.