sssibilancccce...

Some used records I've picked up have ssserioussss isssuessss with sssibilanccce. OK, you get the idea. There's a wicked distortion on "s" sounds only. Otherwise the records sound great. What's up? I have a modest analog setup, well actually WAY modest consisting of the dreaded DD turntable, various isolation tweaks, low end Grado cart, old Rotel phono stage, and decent cabling (have used Harmonic Tech, Silver Audio and Audio Magic) but as it only occurs on certain discs I'm inclined to think it's not my gear. The only cleaning I'm doing right now is with a discwasher and homemade stylus cleaner. Would a vac machine take care of this, or is the record just junk at this point?