Hi Manish,
I’ve only used an iMac Pro 10-core, 64GB, 1TB SSD, Vega 64 for a short time (I don’t own one) but even when being pushed hard rendering a long complicated project it was virtually silent and certainly much quieter than an iMac Retina 5k 4GHz being pushed to it’s ‘limits’. During ‘general’ editing use the system was practically silent unless you put your ear to the rear vent, a near-by Blackmagic unit and the rooms air conditioning were audible but not the iMac Pro.
I’d hazard a guess it’s quieter compared to a tower Dell or HP workstation.
Others have posted reviews online that indicate the new iMac Pro thermal cooling system is very good and noise levels stay low even when the systems CPU’s and GPU’s are pushed hard.