I've done some infrared thermometer spot measurements on my Tesla Inverter. On the hottest day so far this year, with inside the garage is around 85F/30C where the inverter is located, the temps on the silver metal cover is in the low 50C, while the coolant lines are around 54-56C. When the pump output line to the radiator gets to 56C, the fan turns on for maybe 30s before shutting off again.
For the first few days, I could hear what sounded like water trickling/flowing sound from inside the inverter, which others have also mentioned, but it has since disappeared.