First question, as slaw is saying, does your system have sibilance problems when using sources other than the turntable? If so, more information is needed. If not, you might check the alignment
or VTA of your cartridge, that could be a cause of the problem--in my setup, for example, if the cartridge is set up so that it is not parallel to the platter and it is instead leaning forward (i.e., the back is higher than the front, looking from the side), the highs are accentuated.
or VTA of your cartridge, that could be a cause of the problem--in my setup, for example, if the cartridge is set up so that it is not parallel to the platter and it is instead leaning forward (i.e., the back is higher than the front, looking from the side), the highs are accentuated.