For me, running Win10 64-bit (ver 1607), I tracked it down to a scheduled task which runs periodically and launches the Power Efficiency Diagnostics System Analyzer.
If you think this may be the cause, you can quickly check it's the same sound by running
powercfg.exe -energy from an elevated command prompt. After 60 seconds you will hear an audible "click" from the CD- / DVD-ROM drive.
Further checking Task Scheduler for the AnalyzeSystem task under \Microsoft\Windows\Power Efficiency Diagnostics would reveal in the History tab whether the task fired off at the time the click was heard, remembering to allow for the 60s run-time.
Unfortunately the task does not readily lend itself to having its' configuration altered so that it fires less frequently or at more convenient times, but it is possible to disable it, which is what I have chosen to do.
An alternative approach would be to disable the stock MS task and create your own Task with all the parameters you desire.
The usual MSDN searches will provide information on the Analyzer and whether you need or want to have it running on you system.
Hope this helps....