Xenon's example is, by the way, indeed the way I'd handle grenades as attacker. Oh, I'd take Cover first, so they don't notice you bringing out a grenade.
Also, there is no guarantee every runner team and every hostile team has a hacker. And I cannot figure out if a dicepool modifier from noise actually prevents them being triggered.
Personally I miss the SR4 rule from the FAQ, where it says that if you aim at a location to target a person, they still get a dodge test. I mean I can have 25 dodge dice, be running at 170 km/h, and yet someone can turn on a grenade, fire it unopposed and make it explode without me getting any kind of defense roll, only a soak roll.
And yes, 25 dodge dice and 170 km/h running speed are perfectly legal and possible in chargen. I can even manage that with a single character. It is, however, expensive as heck.