Hi Dimitri,
Had a horrible high-pitch noise in the SMPS of my 2215, though was from cold, unbearable (I am only 40 so I still hear this kind of noises...sadly).
Power rails were all spot on and ripple well within spec. Recapped it anyway the other day... now silent as a dead body.
To be honest, at the same I recapped it, I also replaced the MOSFET, with a different/more modern part. So possibly the recap did not fix the issue but the new/different FET did... but I found reports of other "singing" SMPS from other gear of a different design (for example an old 8 bit computers like the TRS-80), where recapping fixed the issue as well.
So I would put my money on the caps rather than the FET...
My 2232 is also singing... so I will be recapping that one as well fairly soon.
FWIW...
Regards,
Vincent Trouilliez
Vince