My iMac keeps waking up the moment I put it to sleep

Question

Alright, so every time I go to put my iMac to sleep it immediately wakes up. Like the screen goes off, you hear the fan power down, then IMMEDIATELY wakes right back up. I've seen Apple's troubleshooting guide for this and nothing seems to apply. I've unplugged my wifi printer entirely, "wake for network access" is off in my energy saver settings, iTunes is closed, Spotlight is not indexing, I've tried unplugging my keyboard and mouse, etc. I'm at a loss here, please help!

Answer 1

Test after each of the following steps that you haven’t already tried:
Step 1
Take all the steps suggested in this support article. That's the starting point for any further effort to solve the problem. Skipping any of those steps may mean that the problem won't be solved. Note that, as stated in the article, the computer  will not sleep if Internet Sharing is enabled.
Step 2
From the menu bar, select
 ▹ System Preferences ▹ Accessibility ▹ Speakable Items: Off
Step 3
Select
 ▹ System Preferences ▹ Bluetooth ▹ Advanced...
and uncheck both boxes marked
Open Bluetooth Setup Assistant at startup if...
Step 4
Reset the SMC.
Step 5
Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards, if applicable. Start up in safe mode and log in to the account with the problem. You must hold down the shift key twice: once when you boot, and again when you log in.
Note: If FileVault is enabled, or if a firmware password is set, or if the boot volume is a Fusion Drive or a software RAID, you can’t do this. Ask for further instructions.
The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.   
Safe mode is much slower to boot and run than normal. Don’t launch any applications at first. If sleep still doesn’t work properly, back up all data and reinstall the OS. After that, if you still have the issue, make a “Genius” appointment at an Apple Store to have the machine tested.
If sleep now works as expected, go on to the next step.
Step 6
Still in safe mode, launch the usual set of applications that are running when you have the problem, including your login items, one at a time, testing after each one. Some applications may not work; skip them. You might be able to identify the cause of the problem this way.
Step 7
If sleep is still working after you’ve launched all the usual applications, reboot as usual (not in safe mode) and test again. If sleep still works, you’re done, at least for the moment.
If you still have the sleep issue after booting out of safe mode, post again.