I've found the problem!
The issue is caused by AIDA64 running in the background and when it attempts to retrieve sensor information from the hard drive in order to report it.
My guess is the drives are in a lower power state but AIDA64 is trying to wake the drive every 20 seconds when it attempts to gather the sensor information for the temperature readings.
This is definitely the cause of the issue,as when I closed AIDA64 the noise stopped, and when I changed the value from 20 to 10 seconds, the noise occurred every 10 seconds.
To change or disable this feature in AIDA64, select File > Preferences > "Hardware Monitoring" and either uncheck the disk temperature box or change the value of the update frequency.
Thanks to those who helped and provided suggestions for things to test.