This happened to me when I first got it and I saw a couple of posts in aussiearcade without solution.
This is not a hardware issue for RaspeberryJamma instead my cabinate wiring was wrong - instead of speaker wires being connected to Speaker +/- in the Jamma edge, it was connected to Speaker+ and 5V most probably because of the amplifier it had required power.
Solution was to remove the wire from 5V and soldering it back to Speaker- on the Jamma edge. Works like a champ.
Cheers
suv
[Solved] Speaker squeaking/screaming RasperryJamma
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