iMac not staying asleep since Mountain Lion upgrade

[zuma022]

Does anyone have any ideas what I could do or check? I upgraded about a month ago and ever since then when I put my iMac to sleep it, I can hear something turning on again. I assume it's the HD starting up. Same sound if you wake up your iMac. The screen usually stays dark though, but the iMac is awake.
The console shows nothing at the second it wakes itself up and so I have no idea what the problem could be. I unplugged all USB and turned off bluetooth. Any ideas? I'd really appreciate it as the iMac is in my bedroom and it is rather annoying.

 

[GGJstudios]

Does anyone have any ideas what I could do or check?

For sleep issues, you may find some useful ideas here:

• Determine why your Mac wakes up from sleep
• OS X Mountain Lion: If your Mac won’t go to or stay in sleep
• Mac OS X: Why your Mac might not sleep or stay in sleep mode
• One sleep problem caused by printers - solved ... and another
• If your Mac isn't sleeping properly and you have gfxCardStatus installed, try uninstalling it.

 

[zuma022]

Thanks for your help. I have finally narrowed it down to being an issue with the wifi. If I turn of wifi on either the phone or the iMac it stays asleep. I have assigned ip addresses for both in the airport utility (apple express 2nd gen) but there seems to be a conflict of some sort. Any ideas how to fix that?

 

[Ice-Cube]

Apparently my MBP is having the same issues. Whenever I opened it up (from sleep), it feels warm like it has never hibernated.