It's entirely possible to make a planet-to-planet trip within the Solar system without having to go faster than light (with our current technology the trip would take several years, but with technological advancement allowing for faster sub-light travel it'd be possible).

At lightspeed it only takes a few hours to get to from Earth to Pluto.

Also, unrelated to the problem but.each of the tours is a year so by the time you get to the game you've been in the military over 3 years (3 tours, basic training, and however long you were on the Rickenbacker).

Plus, the Faster-Than-Light drive is used to travel to other solar systems.Humans are not earthbound in this setting. Even System Shock 1 took place in the orbit of Saturn.

Off Earth but in the solar star system.Goggles spends a year training at locations off Earth before the world's first faster than light ship.Data corruption or intentionally mocking human speech are both possibilities.Or it might be she just talks like that to piss you off.It's possible that her distorted voice is her real voice, while talking in her 'normal' voice is like speaking VEEERRRRYY SLOOOWLY and you're lucky she's even trying.Maybe she just likes sounding like that.Well she is an AI, her voice might sound perfectly normal to her.Evil Gloating takes up a great deal of processing power.

So why is it that after she reveals herself to you, her voice is all distorted again?

SHODAN can speak perfectly normally when she's impersonating Polito.

System shock 2 shodan floating sequence