Probably the previous owner had an aftermarket cooler installed.
You probably got a great deal.
I see no problems unless the fan is unprotected and you have something loose inside the case.
As to dust, the only good way to stop it is to have positive pressure cooling with a filter covering the intake fans.
Otherwise, and occasional use of canned air should be enough.
You might contact Zotac and see what they would charge you for a cover.
Ya i contacted them, they do not offer a replacement. But as long as it works fine im ok with it. I have an antec video card fan i can install right above the graphics card for added airflow.