If your DVR is making a loud grinding or buzzing noise, the noise could either be coming from the cooling fan or from the Hard Drive (HDD).
We first recommend that you check to see if whether the fan is the culprit or if the HDD is the culprit. If you can't tell exactly where the noise is coming from by just listening to the DVR, you may unplug the DVR from its power source and remove the top cover, then plug the DVR back in and turn it on. Removing the top cover will not void your warranty because you are not making any permanent alterations to the DVR, and it is safe to turn on the DVR with the top cover removed for short periods of time.
If the noise is coming from the cooling fan, power off the DVR an use a small phillips screwdriver to loosen or tighten the fan. If the housing on the cooling fan is too tight or too loose, the vibration may cause a buzzing noise. Please also clean out any dust from the fan as well, as excessive dust buildup can cause a buzzing noise.
If the noise is coming from the HDD, then you'll unfortunately need to replace the HDD. When a HDD starts grinding, its either burned out or its about to burn out.