Ask what noise an elephant makes and everyone says the same thing: that brassy trumpet. It is the right answer to the wrong question. Trumpeting is one call out of a repertoire that runs from a bark you could mistake for a dog to a rumble so deep that most of it falls below the bottom edge of human hearing.
This is a guide to the sounds themselves: what each one actually sounds like, the frequency and volume behind it, and the anatomy an elephant uses to produce it. For what the calls mean and how elephants use them socially, that is a separate subject and we cover it in full in how elephants communicate.
The short answer: elephants make at least seven distinct sounds — trumpets, rumbles, roars, barks, snorts, growls and chirps. The trumpet is the famous one, reaching around 470 Hz through the trunk, but the rumble is the one they use most, with a fundamental frequency of roughly 14 to 35 Hz that often falls into infrasound below the 20 Hz limit of human hearing.