Z3801A receivers exhibit loud annoying high pitched
sounds that come from the outer oven controller. Located
on the power supply circuit board, this circuitry sometimes
has a tendency to oscillate. This problem does not cause
any receiver malfunctions.
the noise is definitely noticeable and can be substantially
reduced by the addition of a simple component.
Thanks to Kaoru Suzuki /ex- 7M3LGB of Japan for this