Our 7490's have TB3 ports and we are using both TB16 and Caldigit TS3+ Thunderbolt docks with them.
On our newest 7490's, ones purchased in 2019, as soon as we plug in the TB3 docks, the fans on the laptop crank up and stay cranked up, making a huge amount of noise. This happens whether or not we have anything plugged into the TB3 docks. I could just plug in power to the TB3 dock - no monitors, no mouse or keyboards - and within 30 seconds these 7490s have screaming fans.
As soon as I unplug the TB cable, the computer calms down, and the fans slow down.
Windows isn't doing anything either. Just sitting on the desktop with no programs running. Task Manager shows nothing taking up CPU cycles.
All these laptops are fully updated, basically right out of the box, with Dell Command Update ran and all BIOS updates, driver updates, etc are all run and updated.