Experiences with hot water storage Genvex Vanvex 295

Hello dear readers, we are planning to purchase a Weberhaus passive house built in 2004. The house is equipped with a heat pump type Proxon 630 VP/VPC (also called Genvex GE 630 VP-VPC), sold by Proxon (Zimmermann Lüftung), and a hot water system of the brand Genvex type Vanvex 295 with solar module. We have some questions regarding the practical use and the electricity consumption of the two systems. Perhaps someone uses these systems and can share their experiences with us. We understand the function of the heat pump. We were told that fresh air is drawn in from outside in summer and winter. In winter, the air is warmed by waste heat and a geothermal heat exchanger. Now there is also the hot water system, the extracted water is heated by a compressor and a fan. In peak times, an electric heating rod can be switched on. The current owners of the house explained to us that they have significantly reduced electricity costs since they run the system at night in the so-called party mode. That means the fan runs and keeps the water warm. The family has a cheap night-time electricity tariff. Our questions: Is it plausible to run it at night? Isn't it redundant because the heating ventilation also runs 24 hours? Isn't it loud? We were in the basement where the system is installed while water was being heated and a loud humming was heard. The neighbor said he hears the system at night in his house, but it does not bother him. However, we do not want any trouble in case someone else moves in there. I hope these are not too many questions. I look forward to your answers.