CatBus said:

There's definitely a sound that coincides with the trooper hitting his head on the 77 stereo/surround mix, as those are the only ones I really listen to. The sound isn't really that different from the footstep noises though, so it may well be a well-timed footstep I'm hearing instead of a head bonk. Either way, I don't see the need to add a different sound there. Why should an armored head hitting a hard door sound much different than an armored foot hitting a hard floor?

I just listened to it and I think you are right. The film has audio for the head hitting. I think I always assumed that sound was the crackle of a comm-link.

I believe the rational for the new sound was that a "boink" is what armor would sound like when hitting metal rather then the sound of plastic crackling against the set. The new sound is ultimately pointless.