Thanks, I recall that in the manual but I always thought that MK2 was compatible with everything and being the thicker type was less susceptible to noise.
You would think so, but alas, not: Either the “spare” wires in the Mk.2 cables are picking up the noise, or else the Mk.3 cable is adding a ground. (Not specific to BL3; e.g. BV10->BL18 requires Mk.3 (4-wire) because Mk.2 (8-wire) makes that “data” chirp on volume up/dn.)
I had the same issue taking a regular CAT7 (flat cable), connecting my Beolab3s (with RJ45 to PL connector) and the issue was bad. I could clearly hear an impulse when pressing vol +/-.
Using an 8-wire RJ45-connector Cat.8 (has both pair shield & connector ground) patch cord drove BL18 without noise, ***provided a 4-wire Mk.3 PowerLink cable was used from the BV first***, before the PL-RJ converter dongle. Both flat cable & round worked; shouldn’t matter if the pair twist is to spec. Also Cat.7 should be OK if it’s SFTP (shield&foil-twisted-pair) with the grounded metallic connector head. I chose Cat.8 for the “safety” guarantee (higher data rates = better shielding), but that shouldn’t have mattered. BTW, a (so-called) “Cat.8” female-to-female connector worked OK in that chain, too.
I don’t know if my pl cables are mk2 or mk3, but they are pretty thick and have the litte triangle…
I believe that triangle on the DIN plug was just a B&O convention to help keep track. Third parties, like the folks who made my Mk.3 cable, don’t necessarily follow that convention. (One unverified source claims that generally, the triangle merely points to the positive lead, or to pin 1.)