Which two reptiles have the loudest voices?

Komodo Dragon for one. It growls, hisses and "barks".

Crocodiles and alligators are the only members of the reptile family that have loud voices.

http://www.trivia-library.com/a/animals-random-facts-and-trivia-part-1.htm

YES!! I finally typed the correct string of words into google (not Googol) and the answer that I knew (PBS Komodo Special) was right there almost verbatim!

Yes. Every known reptile in existence has some abiltiy to produce sound. A prime example of this is snakes. They can make a wide variety of hissing sounds, and the rattlesnake,as its name suggests, can rattle its tail from side to side to ward off preadators. It isn't just snakes that can produce noises, Lizards can bark, grunt, hiss and growl, Crocodiles and Alligators can produce low, guttural growls. Generally speaking, unless a reptile is born with any form of vocal defect (although this is very rare) it is capable of producing sound.

(answerbag question, no longer online)

There seems to be some debate on this one. Alligators are claimed to have 90-decibel voices.
https://www.thedodo.com/7-animals-who-love-it-loud-785605994.html#7-animals-who-love-it-loud-785605994.html