While making some noise is a fair tradeoff for some needed speed, it seems that afterburner can be heard from a mile away, even through solid rock.
On top of that, after you stop using it, the sound lingers for another half second, betraying your position all the while. If you pay attention to the shift in where the sound direction is coming from, you can get a good guess as to where the other player is going. These two quirks together are very dangerous for the player using the AB.
Perhaps we can lower the audible range slightly as well as adopt a more D3-like afterburner sound. (there is the inital burst, which is cut short and drowned out by a terminating PUFF to signal the end of an afterburner blast)