led

EDIT/SOLVED: The culprit turned out to be a faulty offbrand 5V 3A DC power adapter. I tried another adapter - incidentally, one that I use to charge my smartphone - and the hissing sound was gone. My other router - also a Raspberry Pi 4B - uses the same power adapter as the one that started malfunctioning/hissing was using, but it is quiet and operates normally. At the very least I draw the following three conclusions: 1) 5V 3A is enough to run a Raspberry Pi 4B as a router with constant heavy TX/RX of at least a couple of terabytes per day. 2) I should be prepared for the other offbrand power adapter - namely the one that came with the OkDo bundle - to fail within a year or so. 3) There are really nice people here that give quick and elaborate responses! Thank you all! 🩵

EDIT/SOLVED: The culprit turned out to be a faulty offbrand 5V 3A DC power adapter. I tried another adapter - incidentally, one that I use to charge my smartphone - and the hissing sound was gone. My other router - also a Raspberry Pi 4B - uses the same power adapter as the one that started malfunctioning/hissing was using, but it is quiet and operates normally. At the very least I draw the following three conclusions:

Semiconductors using gallium nitride tech continue to be a red line for CFIUS.