Mild "jailbars" on 464

[FD]

I have a "medium board" 464 which is a later model. For all intents and purposes working fine - except - it has some light "jailbars" or interference lines? which I don't get on my other machines. Last night I removed the power socket I soldered in (someone had wrecked the traces around it) - and re-did it for the second time. But I am still getting these bars. Probably not as bad as a C64 but rare for an Amstrad. I also replaced the single capacitor on the board near the socket - same result. Same power supply as usual - Retro Computer Shack one - I read the post on the CPC Wiki forum about switchmode power supplies and how they can introduce noise. But it is not a problem on any other machine. Anyway...I may be overreacting, it may just be a quirk of the later models - but thought someone might have an insight? Are the later machines more susceptible?