Let's say that a short in faulty home wiring partially damages the DSL port on a modem... where it still functions, but has intermittent issues. What kind of symptoms would this sort of damage cause? What are the symptoms of a bad DSL modem in general? Would it cause corrupt downloads of files on the computers?
In broad or general terms, problems caused by physical wiring issues will cause the DSL line to drop and disconnect. Depending on what type of DSL modem you have, you can enter the log of your modem and review the errors reported to it.
Other types of physical level errors will "slow down" your DSL line speed (reduce it's bandwidth) to something far below what you expect or are paying for. Using sites like Speedtest are a good starting point to begin a discussion with your ISP.
File downloads are usually handled in an application that performs some rudimentary form of file checking/verification. And that's in addition to the basic error connection provided in TCP (of TCP/IP). So it's unlikely (but possible) that physical level DSL errors cause file corruption. If they did, the application or TCP would more likely catch and resolve that.
So, if you suspect DSL issues, I would recommend: