The loudest pops in that video are most defiantly that of footsteps from the Lying Figure and James, and I suspect you are right in suggesting that they are the original sounds being played back too fast.
As for surround sound, basically all audio positioning in games simulated and has to be that way, in much the same way that most of the visuals in games have to be done by simulation. In regard to these two ports I can't speak from experience since all I've heard of them is from videos with stereo sound, but between reports from others and the few sound files I've seen uploaded elsewhere on this form, I've no doubt these games have surround sound. Reports of things like not being able to tell how far away the sounds of footsteps are coming from suggest a rather shoddily implementation of surround sound though, which I don't doubt either considering how much other sloppy work I have been able to experience for myself in videos of these games.
I checked with several people and the audio speaker are inverted. I just discovered that this bug was already on the PS2 versions. Made the tests you arrange for a monster that is to the left or right of james / heather and you see only the audio of it will be the opposite
Can you find an example in any of the many videos around the net, either of these ports or the PS2 versions? Again, all the videos I've come across the left/right positioning is correct, and I know from first hand experance that the audio positioning is correct on the PC versions.
Even in the first shot of Silent Hill 2 where James is looking at himself in the mirror there is audible clipping while White Noiz is playing. I never did try to disable 5.1 surround sound to see what happens, but at this point I am just hoping that there is a patch on the horizon. If it wasn't for the sluggish controls and audio issues I would actually be alright with this version of Silent Hill 2 on the HD Collection. Even if it is washed out I think that it looks better than the PS2 version.
I've noticed that the sound effects come out from the wrong speaker in the HD Collection. The sounds came from the right directions on the original PlayStation 2 versions of the games. I remember Silent Hill 2 was the first game I playwd on a stereo-speaker television, so I was impressed with being able tell which direction enemies were coming from before they appeared. It's annoying that even this was botched in the HD Collection.