I imagine having a nylon main drive gear in a garage door opener produces the least amount of noise, but unless that thing is regularly lubed with grease to reduce friction (which virtually nobody does), this is what can happen after just a few years if the torsion spring(s) above your garage door aren't perfectly set.
Here's another one. The replacement part can be as little as $20, and that would seem like an inexpensive fix, but it is only if the owner of the opener is an experienced DIYer. The labor for replacing this gear usually costs as much or more than what it would be to replace the entire unit. Whether the homeowner replaces just the nylon gear or a contractor (or the homeowner) installs a new opener, the torsion spring(s) setting should be checked by a garage door specialist, because the opener may be doing too much work.