[zerrantoss]

Recently, after driving for 30 minutes, I would start hearing very loud fan noise blasting at full speed. Initially I thought the sound was coming from a bus or a truck, but it is actually from my X6..
It gets so loud that the pedestrians would turn around and stare.

After deeper investigation, I found a pattern:

When the engine temperature reaches 4 blocks (110 degrees C), the fan starts spinning at maximum speed loudly for 5 seconds. Then it repeats several times until the temperature reaches around 3 blocks (90-100 degrees C).

I asked several mechanics, and they all said this is normal.

I don't really think this is normal as I have never heard the fans so loud before.
I am guessing if it could be one of my temperature sensor failing?

Or could a lack of coolant cause the problem? My coolant level is just a tiny bit above the minimum.

P.S. My warranty already expired, so I am seeking advise here.

Thanks!!

EDIT: Problem found, details and costs posted at #8 below