[morzh]

Well, use a good source and see now if your music is OK or a sinewave tone is clear.
With no new crystal pickup this is the only way to exclude a bad one.

Otherwise we will be chasing ghosts. Granted this is a small amp and if it were in my possession it'd probably take me 1/2 hr to check everything I want in it. But then .... you do nto have the equipment, so get a source, and let us know what kind it is so we figure out where to hook it up.

Meantime you could try to pull the output transistors one by one. First pull one, listen to the music, see if you hear typical half-wave clip sound and if the scratch is still there.
(Do all insertions-extractions with power OFF).
Then put the first transistor in, pull the second one, see if you hear exact same sound as with the other one in.

This way we will know we are not dealing with a bad transistor.
I am quite sure they are OK - "scratchy" does not describe a bad triode, but just to have a quick idea.