Why does the PSU make noise in the PC case, but without it it works quietly?

Question

Frame

Hello. I collect pc. There is a brand new Gigabyte p650b power supply and a mattrexx 55 mesh case.
So, when you install the power supply into the case (without other components), something starts to make a little noise / buzz. Despite the fact that without a case, the power supply works very, very quietly! Also, the volume is affected by the position of the case. If you turn it over so that the power supply is at the top, there is less noise. If the location of the case - lying on its side or in the classic state - there is more noise. At the same time, when you turn the power supply without a case, it is silent in any position.
Tell me, please, what could be the problem and how to fix it?

Answer 1

These are resonances. A good remedy against them (and indeed to reduce the noise of a computer) is to paste over the sidewalls of the case from the inside with thick container cardboard.