How Do You Spell Umming And Ahhing?

I'm not really sure if there is a correct way of spelling those words because technically they aren't really words but when writing that's the way I spelling them.  when people read it they know what you're talking about, which is really the point anyway but if you writing formally (like a paper or something) I would find another word. 

Are you perhaps thinking of the correct term which is "hemming and hawing". Which is a phrase used to describe indecisiveness.