OK, more info:
Ticks appear for me only when remote is connected and FM radio is playing.
Ticks are noticable without doing anything in FM screen.
Higher/lower volume affects ticks volume.
Ticks do not appear on preset-select menu, main menu or context menu, unless while pressing remote/main unit buttons.
scan/preset mode, force mono and specific frequency don't affect the ticking.
Forcing higher CPU freq speeds up the ticks by the appropriate factor.
This might be related to the new FM recording functionality, since FM mode originally was implemented without CPU interference (FM->audiomux->TLV320 bypass->headphone).