I would open it up and see if the fan is dirty. The fans on the 722's rarely run, ( I believe they let them run hot because of complaints of the fan coming on in a bedroom install situation) so I would not think the fan itself is bad, may just be full of dust.
I have my internal fan wired to the 5 volt hdd port so it runs all the time on a low speed and every couple of years it needs to be cleaned.
Micro Center or any other computer store will have them for less the 10 bucks, to me just seems easier then getting a replacement from dish. Don't worry about opening it or breaking the hdd seal as dish is scrapping these at the end of there tour of duty. If you do get a replacement from dish I doubt they will want the old one back.