Sound effects in comics are weird things. Sometimes they work, sometimes they are avoided all together (as in V for Venedetta).
This is quite possibly my second favourite sound effect in a comic I have ever seen
This is from the recent issue of Six Million Dollar Man which - if you are old enough to remember the TV show - gives you an idea of how it should be pronounced. (Not how my wife pronounced it, but she's a big fan of Despicable Me and pronounced like one of Groo's Minions.)
And my favourite onomatopoeia?