iMac 27" (2011) acting strangely during "sleep"?

Question

macOS

Hello.
iMac 27 "(2011) is available. I never turn it off, but at night I send it to sleep mode ... and then the strange begins. There are several behavior scenarios:
1. It happens that after falling asleep, literally after 30-40 seconds, the HDD turns on (heard by the characteristic sounds) and can work like this indefinitely. In this case, the screen does not light up. And if you wake him up at this time, then all the updates of twitter, mail, etc. arrive, that is, as if he was sleeping. By the way, if you wake him up and put him to sleep again, then he falls silent ... for a while.
2. And it happens that he sleeps for a couple of hours, then turns on the HDD (at the same time, the screen also does not light up), rustles for about a minute and turns it off. Then after 30 seconds it turns on the HDD again, rustles for 3-5 minutes and then falls asleep safely. This can be repeated every 2-3 hours. Or maybe turn on the HDD like this and rustle until the morning.
These are the issues that make you uncomfortable. I would like to understand what is the matter and solve it. Somehow I would like to look at the operation log (I just did not find where it is in OS X). What wakes up the HDD.
Perhaps this is the Time Machine, but I have it recently, and this problem was before.
Now is OS X ML. But it was also on Lion.
Thank you. I beg you to help me.

Answer 1

Update to the server and he will stop sleeping at all :)
In general, you never know what he wanted to see there at night? Apparently it happens that it is so catchy - that you can’t fall asleep until the morning. And he takes care of you - the screen does not turn on. Appreciate. And after all, the screen could turn on and, accordingly, the sound. And there it is.

Answer 2

Here is a similar problem.