"heeehhhh" is a word conveying a stalkerish nature. Said by people wishing to establish how stalker-y a person is or by the said stalker, stalking some-one at the time.
"I heard you saw Tim again"
"It was terrible, he was all like "heeehhhh"
*rustling in the buses* "heeehhhh"
Aww crap, It's Tim again!