Strange noise in old Sansui amplifier

Hello Friends. I am repairing an old Sansui amplifier that has a strange noise in both channel
(Channel L noise is stronger than channel R). The model of the amplifier is AU-4900 and the noise is if something is "frying" and then it gets stronger so I have to turn off the amplifier because I think it will destroy the speakers. The amplifier and the loundness board were tested with music apart from equalizer and there is no any noise so I suppose the origin of the failure is in the equalizer. What do you think about all this? Thank you beforehand for your opinions.