Well, is it low or high?  “Hush” is calming, but it’s also a word of caution.  I like that it’s missing from Chapter 8 through 18.  I’m going to label it “low”, but that does not satisfy: what I mean is that it’s a peaceful word for use in the Shire and among elves except when warning others not to notice a certain giant bear.

• 01.004 and the family hushed it up;
• 01.089 Hush!’ said Gandalf.
• 03.029 “Hush, hush! Good People!
• 03.029 “Hush, hush! Good People!
• 07.133 ‘Hush! Take no notice!’
• 19.014 Hush! Hush! Oak, Ash, Thorn!
• 19.014 Hush! Hush! Oak, Ash, Thorn!
• 19.014 Hushed be all water, till dawn is at hand!

Trust Gloin to say exactly what he means.

• 01.095 Gloin speaking: ‘Humph!’ (or some snort more or less like that).

Owls, dwarves, and the goblins of Chapter 5 do it!

• 02.041 hoot twice like a barn-owl
• 02.042 that he could not hoot even once like any kind of owl
• 02.072 or to hoot like an owl,
• 05.149 hooting and hallooing
• 07.096 and the hoot of owls.

Etymologically we learn that this word could represent a hum or a throat-clearing noise.  While elves are high, smelling them is as prosaic as it gets.

• 03.013 “Hmmm! it smells like elves!”

“h’m | hm, int.” OED Online. Oxford University Press, March 2015. Web. 27 May 2015.

Not only is a guffaw a kind of laugh, OED affirms that it is formed echoically from the sound of the laugh it names.  Only giants do it in our work.

• 04.005 They could hear the giants guffawing

“guffaw, v.” OED Online. Oxford University Press, March 2015. Web. 27 May 2015.

While in other stories grumbling could be the warning sign of thunder, in The Hobbit it is always the sound of complaint and earns the “low” tag.

• 02.029 “To think it will soon be June!” grumbled Bilbo,
• 02.039 (and a good deal of grumbling
• 05.149 so soon they went back grumbling
• 06.006 The dwarves were grumbling,
• 06.043 grumbled Bombur;
• 06.057 in spite of his grumbling.
• 07.108 and he was grumbling about it,
• 07.136 The dwarves were inclined to grumble at this,
• 08.026 Don’t start grumbling against orders,
• 08.029 (still grumbling)
• 08.066 he grumbled,
• 08.125 and were not merely grumbling.
• 09.032 and started grumbling loudly
• 09.035 and it was no good grumbling
• 09.038 and grumbled like a large dog
• 09.044 he grumbled.
• 09.066 some grumbled.
• 10.039 There were no more groans or grumbles.
• 12.034 they began to grumble at the hobbit,
• 12.035 If there is any grumbling to be done,
• 13.056 grumbled the hobbit.
• 15.060 he grumbled to himself,
• 16.010 grumbled the fat dwarf.