MyBook won't go to sleep

I have 2 WD Elements and 1 My Book. They are all programmed to go to sleep after 10 minutes and this has been working great for a very long time. Suddenly the MyBook won’t go to sleep anymore and the LED flashes constantly. I have confirmed to the best of my ability that no software is accessing the drive. WD tech support told me that the way the LED is flashing indicates a hardware error. So I decided to retire the drive, which is quite old, and I bought a brand new My Book 4TB. I set this one to go to sleep after 10 minutes and this one as well refuses to go to sleep. The Elements go to sleep but the MyBook just won’t. I have seen numerous people posted about this but I haven’t seen a solution that may be relevant to me. Would appreciate any help. Thanks.

Please check that there are no automatic or continuous backup applications (such as WD Backup, Time Machine, or Windows Backup accessing the drive.

Thanks a lot for your reply. Before posting I did the best I could to confirm that no background apps are running. I disabled antivirus, indexing, and all WD apps. I have checked with Task Manager and cannot find any accesses to the disk. I do have WD Smartware running in the background but it doesn’t even recognize the drive in question. It runs a scheduled backup to a different drive. Don’t know where else to look. Thanks again for your help.

I have done an additional test which I believe is quite effective. I logged out of Windows. The PC remains powered up. Since Windows is logged out there should be no background apps running at all. After the sleep timeout my Elements drive went to sleep but the My Book still did not. Since there are no apps running there should be nothing accessing the drive and yet it does not go to sleep. Does this mean the drive is faulty? Would appreciate any help.