Hello Peter,

Some power supplies are particular noisy.
I use a wall wart type with a transformer (no switching type).
But again as you found out, noise differs from one model to the other.
It is a pity that wall warts with transformers are now banned in the EU.
It gets exceedingly difficult to source them.

Peter, which transistor are you using for the emitter follower?

73,
Roelof, pa0rdt