You can absolutely remove the sound already. You need to grab a silent ogg file. When you go there, just right click the Silence.ogg link under the little audio player plugin and save the file to your drive. You'll need to make 2 copies, one named teletrans3.ogg and teletrans4.ogg for the the other one. After that, you'll need to put them in a very specific location:
<Game folder>\data\Sound\Ogg\Powers
So you'd make a data folder in the game's main folder which for most folks is probably C:\Games\City of Heroes if they've been following the general advice to avoid most of the common issues. Inside that, you'd make a Sound folder and so on. Drop those silent ogg files in the Powers folder and when next you launch the game, you have a silent teleport.
You can also silence other things. I've silenced portal noises, for example, so standing in Peregrine Island at a portal waiting for the team doesn't give me a headache. You can find a lot more in this post from the old forums.