IMac i7 - Strange CPU-fan problem!

Hi,
my name is Chris and I'm living in Germany. Sorry for my pigeon english, I'm not very good in languages... Nevertheless I will try to describe my problem.
I have received my iMac last saturday. It's an i7 with 2TB hard drive. On sunday suddenly the CPU-fan went nuts, spinning with about 3500 rpm. At that time there was no heavy CPU load at all.
Neither P-RAM- nor SMC-resets fixed the problem, the CPU-fan was running at full speed all the time. On monday morning (the i7 was switched during the night), the problem was still persisting. Hence, I contacted Apple and they promised to send me a replacement for the i7 in about three weeks.
Later on this monday, I received a package with additional 4GB of memory I had ordered for the iMac. Although the iMac was making noise comparable to a 747, I decided to build in the additional 4GB of RAM, just to play a bit around with an "8GB machine". The assembly of the additional memory was pretty easy, basically everything was working fine (memory wise). But the CPU-fan was still continuously at around 3500 rpm.
Afterwards, I decided to clean up the computer a bit by using the "automatic" script within "Onyx". I started the procedure and left the room.
When I came back about 1 hour later, there was total silence in the room. In first instance I wasn't surprised very much, because the iMac was obviously in the sleep mode. But I was really surprised when I woke it up again: The CPU- fan was back to normal, spinning with 940rpm. Almost completely silent.
Any ideas what happened? Can there be a connection between the "fan-went-nuts-issue" and the Onyx scripts?
What shall I do? My iMac is behaving now, but I have already ordered replacement...
Best wishes,
Chris

Yes, I have seen this thread, thank you.
When the CPU-fan started to spin at 3800, one of the first thing I tried was putting the iMac into the sleep mode. After I had done so, I woke it up back again almost immediately (about 1 minute later) by pressing the space bar. But for some reason, the iMac woke (with normal fan noise) and then immediately fall back into sleep (after being about 10 seconds awake). A "proper wake up" was not possible, since it was sort of an infinitely loop of waking up and falling asleep. A reboot via the power button was necessary, whereby the fan went back to 3800 rpm.
And then I performed this Onyx-run (as mentioned in my first post), and afterwards the iMac went to sleep mode automatically. It stayed in the sleep mode for about an hour or so, and after my next wake up call it was cured.
Really strange. Either it was cured by the maintenance-things Onyx did to the cache/system files, or by being in the sleep mode for about one hour. I also can't exclude influence of our Lord, since I was behaving in the last year...
Somehow I have lost my trust in that machine. Even after the fan went back to normal behavior I am still not sure if I should cancel the replacement order... I am open for recommendations from your side.
Best wishes,
Chris

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