Almost 90% of the time Phase Riflers don't even know that I'm standing right behind them XD Even a group of 3 Phase Rifles users that were camping on Pentagon on the top Floor didn't notice me when I was walking back and forth behind their backs.
The ARC is so noisy it's basically useless. It's great for noobs that don't know what that sound is, but you'll have a hard time against veteran players.
Why would you go into Stealth mode that close near the opponent? If they are in hearing distance you might as well just engage the gunfight and ambush them rather going invisible.
You're supposed to turn invisible before sneaking behind the opponent, that way the sound can't be heard ^_^ There is a specific radius to able to pick up the sound. I once tried to calculate it using the ASE distance meter to determine what the distance was. Can't remember the exact distance though :X