Post isn't clear about the constraints. Does s/he have to keep it in place, or can he remove it (to a workshop, for instance)?
Noise is caused by friction. First thing I'd do is make sure there is no grease nor oil in the lock. Solvents such as benzene would wash away most of those, and carbon tetrachloride would probably wash away anything the benzene didn't. If your character can put the lock into a bath of either (or perhaps a combination) and heat it (without blowing himself up - CCl4 isn't flammable, but bz certainly is) that is called degreasing. Even in 1850, vapor degreasing where parts were hung above a heated solvent (and the solvent condensed onto the cooler part and rinsed them) was well known. Note that paint would be removed, as would labels, so it might change the exterior appearance... As far as some process which would rapidly corrode the contact surfaces so that operating the lock became noisy, that is a problem and depends on the lock's design. In general, I'd guess that what you want to do is go from two smooth metal surfaces that slide by each other, to two rough rusted surfaces where there's a lot of friction. First idea that comes to me (if you're not satisfied with a simple solvent cleaning) is salt water and an electrical current. That would really kick the rusting into high gear. And the bigger the battery you use, the faster the rusting. Incidentally, saying that acid dissolves rust is true, but its not a black/white thing. pH 5 is much more aggressive than pH 7, and little rust will be dissolved. Anyway, even if it is, the surface left behind will be rough and MUCH more prone to flash rusting, so a quick acid rinse might also help. Problem is, these treatments only work if the liquid comes in contact with the desired surfaces. That is, the lock probably should be operated (workshop) as it's chemically attacked/cleaned. Its fairly obvious that two surfaces in tight contact won't allow any of these liquids to penetrate. Heating might help, idk. Which brings up just the idea of heating the lock to really high temperatures while exposing it to oxygen gas (even better, I think, would be a little water vapor too). Using a perfume (spray) applicator to both clean and another to apply corrosive would possibly work if the lock can't be moved (and it might be faster even if it can be). I'd not worry too much about the details here, there aren't that many people who would know, one way or the other, whether just solvent cleaning would or would not be enough, (I certainly don't) to make opening the lock noisy, and fewer still whether a quick electrochemical treatment after that would finish the job. Just has to be chemically plausible, and I'd say solvent rinse followed by salt solution and running electricity thru it, would certainly seem plausible to 99.99% of your readers.