If you DVD drive is making more than the usual whirring and spinning noises and actually damaging disks, sorry to say this, but it’s toast. Using a cleaning disk won’t help, as they only clean the lens of the laser and try to remove dust from the drive. If the drive is making that much noise, there is physical damage that a cleaning disk can’t fix. I’d guess the whole DVD drive needs to be replaced with a new unit.
The issue is finding someone to do the work. Some local stores in Missoula may advertise as Apple dealers, but for repairs, they will send your Mac out to be fixed. There should be one authorized service center in Missoula that will do the work for you here in town. Go to Apple – Find Locations and find a local Apple Authorized service center. They can order a new DVD drive and install it.
Beware: it might be expensive, and if you don’t have AppleCare coverage, it might cost more than the iMac is worth. But if the iMac is otherwise running good, keep it and get it fixed.