Well, you can strike lucky. Years ago I bought an FM radio tuner made by JVC. It whistled under my favourite music station. I opened it up and saw there was no ‘multiplex’ filter - just a factory fitted bypass wire.
Contacted JVC in UK - their reply was ‘There are no user serviceable parts and opening the product will invalidate the guarantee’
So I wrote direct to JVC in Japan. In three days an envelope arrived containing the filter coil plus clear note on how to remove the bypass and fit the coil.
Radio worked beautifully after that, and still does.
I have felt well-disposed towards JVC ever since.