I have a Panasonic landline (wireless) setup in my home. They have multiple charging stations, 2 remote bases, and one actual base station. They’ve worked reliably for at least 8 years, and I know Panasonic is excellent quality.
Recently, I’ve noticed one handset hisses during charging. It does this regardless of whether or not there are batteries in it, and after removing the back, I cannot tell where the noise is coming from. I tried holding down various components within it to see if I could narrow it down - to no avail. There are a couple big ICs and two PTH caps. The rest are SMD, and the PTH caps are held down by white adhesive.
Some digging online suggests that capacitors can hiss, piezoelectrically, but that seems limited to ceramic caps, not electrolytic ones. There are no vents and no bulging on either PTH cap, and besides the color & specs, they resemble the one pictured below. Any thoughts?
Edit: model is an older version of the “dect 6.0 plus” / “tga401” Edit:: no components are hot to the touch when noise is made.