Maybe this is quite a stupid question, but anyways:

I made an lmd_door and each time you use it I want it to make a sound (sound/movers/doors/door_huge_start.mp3). So I tried using the target key on the door, didn't work, and tried using a target_relay that targets both the door and the sound, it worked, but the sound kept playing over and over again. What's wrong? It'd be easier if lmd_door had a soundset key.. ¬¬

You should just be able to have the lmd_door's target point to a target_speaker placed near the door itself. Do you have spawnflags,1 on the target_speaker? That will loop the sound too.

It works but it doesn't loop the sound, not even with spawnflags 1, i'll try to change the sound file.