Elements on iMac won't go to sleep

I have a 1TB Elements as the startup drive for my iMac using El Capitan. When I put the computer to sleep, I would like the drive to sleep also. But it continues to be accessed by the iMac. I have turned off everything I can find, but it still keeps chugging along. Any ideas on this would be very helpful.

Does the hard drive shut down when the computer is powered-off instead? If so, then there could be a system setting feeding power to your unit’s USB port, preventing sleep.

Check your System Control-> Energy Settings. However, this will affect all external hard drives.

Thanks for the reply. The drive does shut down when the computer is off. I have all the Energy Settings turned way down, no automatic mail checking, etc. I didn’t shut off my wireless network, so I’ll try that next.