I had a question in my last session that I coulnd`t answer. How loud are the techpriests when moving? and the servitors? Is possible for a gigantic metallic person to sneak?

Yes, it's possible for tech-priests to be stealthy. Admittedly, they usually don't bother, nor is it common for them to be trained in stealth, and they usually don't have very good agility, either. As a result, the average tech-priest generally isn't particularly stealthy.

Servitors are only stealthy if they're programmed and directed with stealth in mind. They usually aren't.

However, as members of the AdMech, tech-priests (of sufficient rank/connections) can get access to gear that augments stealth.

I would assume any tech-priest interested in being stealthy would invest in stummers, chameleoline, blur suits, synskin stealth suits, etc. Such gear can also be used to augment servitors, but that would be unusual.

I like your answer but my doubt is actually if the tech-priest in general are loud creatures with all those implanted mechanisms . When they move, talk or just being still.

A tech-priest just standing there? Probably not particularly loud.

It also depends, to an extent, on what augmentation they have undergone and the quality of those implants/augments.

For example, a poor quality respiratory replacement is going to be louder than a regular person breathing, but good or best respiratory replacements won't make any extra noise. A common quality respiratory replacement might be on the louder end of normal breathing, with perhaps a touch like of Vader-breathing.

Walking? Probably no louder that someone wearing heavy boots, unless they've got lousy augments.

Talking? Depending on augments and implants, that could be a Vader-voice to a Grievous-voice, or a normal voice. Also depends on the tech-priest's personal preferences.

Frankly, it's kind of a soft spot in the lore, but I wouldn't make a tech-priest automatically noisier than anyone else. I mean, I'd say that someone who's heavily augmented is probably going to go for better augments as well. In addition, I'd probably say that with an adequate hearing-based Awareness test, you'd be able to tell that someone is augmented (or wearing power armor) if they're moving around a bit - although this is going to be easier in a natural environment, not a manufactured/artificial one, and probably nearly impossible in an area with any sort of noise from machinery or air circulation systems.

Doesn't the machine trait mean that you can survive in the void and (presumably) the character isn't actually breathing any more? In that case I'd say it is possible that the character might be quieter than a regular person when standing still.

I imagine a lot of the implants, particularly mechandrites make a low grade buzzing noise when moving but honestly that is mostly for the intimidation factor. I'd say silent implants are possible because there are stealth based servitors.

Doesn't the machine trait mean that you can survive in the void and (presumably) the character isn't actually breathing any more? In that case I'd say it is possible that the character might be quieter than a regular person when standing still.

I imagine a lot of the implants, particularly mechandrites make a low grade buzzing noise when moving but honestly that is mostly for the intimidation factor. I'd say silent implants are possible because there are stealth based servitors.

That's the Machine Trait ... which isn't part of the Mechanicus Implants, and although I expect most tech-priests to eventually acquire at least one level of it, usually in the form of The Flesh is Weak advances, if not more, it's not automatic for them or anybody else, with or without respiratory implants.