So after a while and...1 DOA and two visits from tech with replacement service for the CPU fan etc.. I have found the answer. The ONLY answer is to just accept that the CPU fan selected for this set up by DELL is wrongfully designed or defective in some way. The way (like i did) is to get angry and purchase a proper fan to install by yourself. For me a Noctua Nf-a8 PWN fan worked like a charm and i can claim at last my peace of mind. After an XPS 9570 which had its own issues like any of this line and a fresh inspiron 3881mt i can say that im really disappointed first of at my self cause i kind of had this little demon whispering at my ear during the purchase that I'm maybe gonna have issues and secondly I'm really disappointed by DELL. I can not accept the overpriced setups with low quality components. You are going to tell "hey bud so why did you went for that setup....well we are living times of war. I had to. On the other hand i want to give huge credit to the couple of agents that actually tried to help however they could. Kudos to the DELL agents in the DELL community. To the Mother DELL tho.....one word. WHY. 
Hello there.  A couple of days ago i've purchased a Dell 3881 mt i7 desktop. From the boot up alone the fan noise was like something is not installed properly or something. So i used after i've called service DOA.  Then the new unit arrived and i've boot it up patched al the updates.....The same issue. The noise is like something is touching something. After a call with the service again they have told me that (because it is a new unit) this is normal. I can hear the noise in the next room. It is not possible to work like this.  So the question is if i replace the FAN my self with a new one will there be a warranty loss? If yes i will returne the machine and take my money back. Plus i need some proposals of compatible fans. The unit costs and to have such issues is kind of disappointing. DELL why do you not care about fans? Why you don't care about decibels in your user ears? This comes from an XPS 9570 (i love it tho) user which also have had such problems with the fans. (plus i have had some BSOD's - "dpc_watchdog_violation - to the both units) Love Jimmy
inspiron 3881 fan unacceptable!