My Multiplus 2 is making a constant hum/buzz. I expect that - sort of normal with toroidal transformers. However, in the evenings the grid AC becomes a bit high (240-245 V), and the humming becomes louder. When should I start worrying?
Measuring with the NIOSH SLM app the buzz is about 38.6 dB(A) when the grid is connected (V_ac_in= 243 V), and 33 dB(A) when the grid is disconnected.
Using an app creatively called “Spectrum”, it seems like the buzz is at 200 Hz. Why would that be (I expected 50 Hz, which is the grid frequency)? My knowledge of toroidal transformers is lacking, so I’m mostly curious. I guess it could be a limitation of the app.