When reduced to its endoskeleton, the Terminator makes quite a noise as it manoeuvres around. There's no way skin could conceal such a sound. Ever crack your knuckles? Or grind your teeth? The noise is clearly audible to nearby people, especially in quiet locations. That we hear none of the Terminator's clanking and grinding when it's in almost-silent apartments, is slightly suspect, IMO.
Having the endoskeleton noises present throughout the film would have added another layer, actually. People could look at the Terminator in bewilderment as they see a regular man emitting robot-like sounds. Perhaps T would be forced to avoid quiet places, lest its cover be blown.
This thought crossed my mind once or twice over the years. I then took in to consideration the events that took place before and after the T-800 began making the noises.
No noise:
T-800 pressumably fresh from the production line, programmed objectives and sent back to 1984. Brand new machine, fresh hardware/software.
Noise:
After multiple road collisions, both direct and indirect. Multiple gunshots. Explosion, which damaged the T-800 enough to slow it significantly (broken foot etc.
*Fire* The T-800 emerged from the flames and the noises begin. Heat causes metal to expand, causing more friction, causing more noise. Also any lubricant throughout the exoskeleton for the metal moving parts would have dried/burnt while exposed to the flames. I do believe a certain amount of grease is required in most machines with moving metal parts/motors. Ever run a fan without it? Or hear an old PC with unlubricated fans? Very loud. Like the original Xbox 360.
I could be wrong and I'm aware it's only a movie (one of my all time favourites), but that's just my opinion, hehe.
It's possible the living flesh is actually designed to provide a kind of dynamic lubrication to the endoskeleton. You might even go so far as to say that it helps circulate the flesh's blood as well.
Along with it's outer skin the Terminator had sound cancellation hardware installed to prevent any metallic, clanking sound..Yes, in the future such technology STILL exists.