KiOgon

OK not frequency as such - how often does it tick?

Have you tried it in different places/buildings? It could be RFI, something in your house or area. What frequency is the tick?

Deathwatch Beetle? - " Deathwatch beetle alert. Q We have deathwatch beetle, and I am in a quandary about what to do. Although I can't see obvious bore holes, I heard their telltale clicking during April and May." (From The Telegraph) Seriously though, could be anything from the pick up's windings through to wiring, pots, cap. or jack socket. As it's a Jazz bass, this may not apply: http://www.buildingconservation.com/articles/beetle/beetle.html

Not Yamaha's nut fault - those phat b'stards were never going in that slot

Don't send 'em round here then, my fence has just cost me >£2.5k

A wise move I reckon

The photo showing the neck heel also shows a pot and wiring, that ain't a CTS pot and the grey screened lead shown soldered to the pot ain't Fender either, so I doubt the pick ups are. POS IMHO.

Of course if you don't like chicken you could try GHS Fast Fret https://www.gear4music.com/Guitar-and-Bass/GHS-Fast-Fret-String-Lubricant-4oz/7CT?origin=product-ads&utm_campaign=*PLA+Shop+-+All+Products&utm_medium=vertical_search&network=google&adgroup=**All+Products&merchant_id=1279443&product_id=9533d1&product_country=GB&product_partition_id=29215885694&gclid=EAIaIQobChMIurjMnuv_2QIVSpPtCh0nIAmeEAQYASABEgJA7vD_BwE Other lubes are available

If it was mine, I would make sure I had compatible varnish and thinners by testing on a hidden area, maybe under a tuner, make sure there's no reaction between old and new. Then apply thinned varnish to the cracks, gaps and especially under the decal where it's lifting, pushing the decal down flat onto the wet surface underneath until it sticks. When dry, build up layers as required, finishing with a coat or three over the whole area. Patience will be required!

DodoJuice, maybe after the T-cut https://www.amazon.co.uk/Dodo-Juice-DJBVP30-Carnauba-Velvet/dp/B003JJ3GX2/ref=pd_rhf_ee_s_pd_session_scf_1_5?_encoding=UTF8&pd_rd_i=B003JJ3GX2&pd_rd_r=SDW8MC8PS66YGJ4Q5MND&pd_rd_w=5M1O3&pd_rd_wg=28mN6&pf_rd_i=desktop-rhf&pf_rd_m=A3P5ROKL5A1OLE&pf_rd_p=1667995087&pf_rd_r=SDW8MC8PS66YGJ4Q5MND&pf_rd_s=desktop-rhf&pf_rd_t=40701&psc=1&refRID=SDW8MC8PS66YGJ4Q5MND

http://guitardaterproject.org/fender.aspx

Or Halloween Pumpkin?

Technically - Nylon strings won't work on a electric bass or guitar You mean nylon covered, maybe tape wound?

Dodo Juice, a little goes a long way; https://www.amazon.co.uk/Dodo-Juice-DJBVP30-Carnauba-Velvet/dp/B003JJ3GX2/ref=pd_rhf_ee_s_pd_session_scf_1_5?_encoding=UTF8&pd_rd_i=B003JJ3GX2&pd_rd_r=SDW8MC8PS66YGJ4Q5MND&pd_rd_w=5M1O3&pd_rd_wg=28mN6&pf_rd_i=desktop-rhf&pf_rd_m=A3P5ROKL5A1OLE&pf_rd_p=1667995087&pf_rd_r=SDW8MC8PS66YGJ4Q5MND&pf_rd_s=desktop-rhf&pf_rd_t=40701&psc=1&refRID=SDW8MC8PS66YGJ4Q5MND