I think the wooshy sound from the Adventure Time opening used to do it for me, especially when I was wearing headphones (I don't know why that particular sound was so effective), but I think I'm desensitised to it by now.
I don't like whispering, but there's a feeling I get when teachers sit down and calmly explain something to me in a low voice that really makes my toes curl.
Toe curling generally indicates either embarrassment or sexual excitement. Actually I'm pretty sure the response to a woman whispering lustily into your ear is also sexual, although that doesn't seem to be true for all tingles.
The thing is... how can I put this...
The thing I want to compare this to is the mechanism cats have where they intellectually freeze up when you pinch the back of their neck, because that's how their mother would carry them around, they freeze to stop from hurting themselves (don't pick adults up by the back of the neck, you will hurt them).
I suspect it's a similar thing but for people, I think it's basically like an instinctual reaction for babies to relax when exposed to certain soothing stimuli, like a softly spoken voice, or maybe the sound of someone stroking your head?
Whenever it triggers I feel really relaxed, I sort of want to stretch or curl up my neck and extremities. That's, kind of what it's like for me.