The most common issue that causes the DVR+(CM-7500GB16) not to record, have choppy video, audio dropout, and behave strangely is usually a defective or unsupported hard drive. As of January 2017, we only recommend 1 External Hard Drive. Toshiba Product ID: HDTB310XK3AA
Many off the shelf hard drives will work fine with the DVR+ (CM-7500GB16), but it's not practical for Channel Master to test every single drive on the market for Ideal performance. We strongly suggest using the hard drive that we recommend. You may try any other drive at your own risk, but the downside of this is if it does not work you may need to try another one.