I use a Souther, and when this happens to me I clean the tracks and the problem goes away. You might check and see if your arm gets in a bind along the track.
Signs of cartridge wear
I have a Helikon with 2K hours that becomes sibilant on transients in the inner third of LPs. This is a bit odd, as I'm using a linear tracking arm set up for perfect tangency across the full radius of the platter. Raising VTF to 2.3g (about 20% higher than Lyra's suggested maximum VTF) eliminates the problem. Is this a sign of stylus wear, suspension wear, or perhaps of both?