Turntable sibilance


Okay turntable Yodas, what is the primary cause of sibilance in vinyl replay? Obviously some records are badly cut & it's in the grooves, but I seem to have an inordinate amount of it.

I have a Shelter 501 mk 11 cartridge on a Rega RB 250 arm on a Nottingham Analogue Studios Horizon table. Running vtf at 1.8, but changing it in either direction makes negligible difference. Excuse my ignorance, but how do you change the vta on these arms, & might that be the issue? Setup was done by reputable hi fi store, spirit level says table is flat. The green sliding horizontal tracking adjuster doesn't seem to much either.

Any suggestions would be received gratefully.
houseofhits
What tonearm cable are you using? You may sibilance as a result of earth grounding/lack/inadequacy thereof.
Have a listen to a Townshend Trough turntable and they cut out sibilance almost entirely which makes you think that you have lost out on treble - in other words it could be an arm issue - try out the isolator as Markpao says
+1 Viridian, I have had a cart./tonearm mismatch and could not solve for sibilance - Blackbird cartridge on a hadcock tonearm. Low compliance cartridge and low to medium mass tonearm in my case.

The same cartridge on a vector 4 has no sibilance at all.
You may be onto something there. The arm was rewired with Cardas wire, but unlike every other source in my system, which are dead quiet, there is low level 50 cycles hum (our 50 cycles in Australia is your 60 cycles) with the table. Grounding the earth wire has zero effect. Now I find out that Rega have a system where everything is grounded via the right channel wire.
Seems counterintuitive that an earthing inadequacy would produce sibilance but you're probably right. I might be able to solve two issues with one fix, although not sure how yet.
Sorry the response re tonearm wiring should have been in response to Parrotbee, not Pops.
I have a 501 II on a Rega as well. I have 9 additional grams at the headshell. It works.