Internal HDD won't go to sleep

[Geoff BANNOCKBURN]

One or more of my 4x Mac internal hard drives will not stop spinning despite Energy Saver settings that should put the screen and hard drives to sleep after about 5-10 minutes of inactivity. The following System Preference Energy Saver boxes are ticked:
- Put hard disks to sleep when possible;
- Wake for Ethernet network access; and
- Allow power button to put computer to sleep.

This computer is a Mac Pro with 2 x 2.66 GHz Dual-Core Intel Xeon and 4 GB 667 MHz DDR2 FB-DIMM running Mac OS X Lion 10.7.3
My OS runs on the original Mac HD 250Gb, with most of my data on an internal 3TB HDD, and a small amount of data on 1TB and 500GB internal HDDs.

 

[Kaveman]

Are you sure its not the power supply fans, with that number of drives I think the draw on the power supply is such that it trips it over the limit.