: This. I'm no expert, but I'm pretty sure Sniper Rifles (especially Halo's)
: are going to be stupid loud. Even suppressed. And it's not like it HAS to
: be quiet. It's a Sniper Rifle. The whole point is you're hitting something
: from REALLY far away. It doesn't matter if they hear you if they can't hit
: back.

Sure they can. If they hear you, they can estimate where you're coming from and find cover. Ineffective. If they don't hear you, they have no idea what just happened. It would take a bit longer to realize bullet wound, let alone that it's from a distance, let alone the angle. Actually they might get angle before distance, but finding effective cover requires both.
Plus you don't want to risk that they might in fact have a way to hit back. Unless you know they don't have their own sniper.

Sniper v sniper wars are fascinating. There have been a few movies, iirc, that depict the strategy nicely. Can't remember which movies now though :P war movies, for certain.