There are two types of "hmm".

1st type:

What do you want to eat?
hmm.. I'll have the qagh.

2nd type:

So, what's it gonna be? hmm? will you eat the qagh?

I think that we could say with certainty, that both {ghghgh} and {Hu'ma/Hu'mI/Hu} express the 1st type of terran "hmm".

But do they express the 2nd type too?

~ Dana'an
remain klingon