The wall wart supplied with my ATS-909 introduces some noise to the
receiver audio. Are there any ways to suppress the noise? Ferrite
beads in the leads?

The noise is very annoying, since I like using the ATS-909 with an
external power supply. The receiver eats batteries for breakfast, and
SW reception suffers severely as soon as 3/4 or less battery power is
available. When I connect the wall wart, reception and signal strength
improve dramatically, but so does noise. It does not matter when
listening to strong BC signals, but listening to weak signals becomes
a pain.

Many thanks for your tips,

t3000