The fan in the earlier MultiPlus-II, EasySolar-II and Quattro-II units can be noisy, especially at low fan speeds.
The electronics design in the recent MP-II/ES-II/QUA-II units has been improved, fixing this problem.
For the earlier units, we now have a small PCBA available that can be retrofitted to an existing unit without having to take a unit from the wall.
Installing the PCBA, MGR50 MultiPlus-II 3kVA-5kVA fan PWM converter 40kHz Retrofit Kit Victron Energy (SPR00090) will reduce noise for all fan speeds except full speed. In other words, at 100% fan speed, there is no difference between the old and the new situation.