Loud Grumbling (Stomach Rumbling-Like) Sounds coming from iMac?

Question

Hello,
I bought a 27 inch iMac around the beginning of June and have been impressed with it ever since. As a frequent customer of Apple's I have purchased alot of Apple's products over the years including 'The New Ipad', 2 iPhone 5, Apple TV and some older generation iPhones.
     When I first purchased this iMac i noticed a small sound comming from my iMac. I ignored the sound as I am a previous PC user and was used to the loud Computer sounds. The sound exculated more and more until nowit is easily heard and I can even hear it a couple of feet away from my computer. I can also hear it even if my display is off (I can even hear it now). Its very iritating and can only be closely descirbed as a Stomach-Like rumbling noise. I began to worry that this may become a bigger problem like Hard Drive failure or some other types of problem as these sounds do tend to warn me and so took the precuation of taking my iMac into the Apple Store, White City, Westfields in London. The technician there ran some quick tests and tried to find the sound however above the music in the store and the hastle of people going forth and back, was unable to hear it. We asked her if she could take it inside at the back of the store which she did. She ran a few test (Note that we werent with her when she went to the back of the store) and ran a few tests one where she maxed out the CPU and tried to see if any fault was visible or heard. She was unable to locate the sound and therefore had no choice but to return it to us. (Also note that we have an extended 3 year Apple Care Agrement).
     I was dissapointed and hoped maybe it may stop when i set it up again at home but was unhappy when the sound began to reoccur. This happens often however once it begans its a while until it stops and can be very iritating especialy when working infront of it or trying to focus on some work on screen. I just wanted to see if anyone had any suggestions or any other solutions experiences like me with this peculiar sounds because as far as I can rememebr paying over £1,600 and paying around £135 for an extended waurentee and being a loyal customer who has purchased alot of apples products I would like my product to be as described on the website. Noiseless (Or Silent). I hope that theres a simple explanation maybe a hard drive fault (As it happend in 2009) and if so i hope Apple has the decency to recall its products or hard drives for new ones (faultless i hope) otherwise i think that this could trigger some legal matter into the description of the supposingly 'noisless iMac'.
     Also I noticed that many others have this problem and hope that maybe even an apple techinicain can help because this does effect my thoguhts about Apple and i hope that sometime, somehow someone will help.
Thank You
I have not tampered with anything on the system by neither opening it or tryign to fix it myself and therfore not liable.

Answer 1

I went to Apple told them there was a problem. They said it was the fan after we heard the noise. So they took it in and said taht they would replae all fans. After 3 days they call to say the iMac is ready. So i go in and they tell me that the problem was with the optical drive and the optical drive fan so they replaced all the fans and the optical hard drive.
Took it home and......problem started all over again. So far they've replaced the Hard Drive (2TB), all 4 fans and the optical drive and the issue is still not solved.... This is becomign really annoying and I'm fed up because ifits taking so much of my time, money and my work because I dont have to the iMac to use and im using a Sony Laptop instead. Any Suggestions please??
Thank you