Laundry smells musty though freshly washed?

It always happened to me that laundry, which just came freshly washed out of the machine, smelled strangely musty.

Then I read the solution somewhere:

This "Muff" should come because you have washed too long at too low a temperature. This is very praiseworthy to wash everything with at most 40 degrees and certainly enough, but this musty smell in the machine you get away by whistling from time to time to the environment and a wash (towels or underwear) at 90 Degree cheered.

GET RID OF SOUR SMELLING LAUNDRY | FRESH SMELLING CLOTHES AND TOWELS | April 2024