Wires don't make noise and capacitors don't vibrate.
The simple answer is that the fan in the converter is noisy. If so, and if this is a new development, you might be able to replace the fan. On the other hand, it might just be a noisy design.
There is one other possibility. The largest component in the converter is the transformer. The transformer is constructed with primary and secondary coils of wire around a core laminated of many "E" shaped layers in alternating directions. There are usually either 2 or 4 bolts or large machine screws holding the laminations together. The entire assembly is then dipped in varnish. The varnish tends to hold the stack together and also keeps the screws from loosening.
If things do get loose, the electromagnetism causes the laminations to vibrate at 60 Hz. If you can get to the screws, you might be able to tighten them, but the varnish might make it a little bit difficult.
Retired electronics engineer. Avid paddler & birder.
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