Did the noise start immediately after the work was done? If not, they're probably not related. The only moving parts within your Mac Mini are the cooling fan and hard drive, and which one is causing the noise depends on what it sounds like. Does it sound like friction, grinding? Just a loud humming? The former would indicate an issue, most likely with the fan (as when a hard drive makes that kind of noise, it usually isn't functional), while the latter indicates that your machine is working harder to keep itself cool - which would point to a change in the way you're using the machine (utilizing more resources than previously) or an issue with heat.
