HowieBass

It's OK to use a pick, honestly!

Do you get the 'beating' happening if you mute the other strings? I'd suspect sympathetic ringing from the other strings (especially the D). If muting the other strings cures the problem, maybe try something like a fret wrap just behind the nut?

First time I saw one of these was by the bass player in Little Dragon... https://youtu.be/X0IslF4nSSk

That'll teach me to drop straight into my fantasy without reading all the rules! 😁 I bet I'll even have to buy a damn Lottery ticket too 😂

A year-of-birth bass, exactly like this... 😁

I've always liked Barry Adamson's work with Magazine...

I use metal polish to get rid of all manner of residue/marks on a variety of surfaces.

More likely the truss rod isn't tight enough... it sounds to me like you might have a tad too much relief...

Because if you do it based on recommended measurements (I use the Fender guide) you have to set relief first because string height above the frets is affected by how much relief there is. Refer to any bass setup guide and it'll advise you to set relief first. If, after correctly setting relief and action, you find that fret buzz still occurs, then it's time to start checking for high/uneven frets.

A business card (cardboard) is the thickness you're looking for with neck relief, a plastic credit card is too thick. Fret buzz near the nut suggests there's too little relief; fret buzz at the dusty end suggest there's too much relief. You should only set the action (saddle height) once the relief has been set correctly.

You might have a touch too much relief. Try reducing it a little and see if that cures your problem.

Regarding re-stringing... I normally go through a setup routine to check if a change of string has affected the relief and intonation and that's even when it's the same gauge. As I said earlier, buzzing high up is usually due to too much relief. Clearly whenever you fret a string you're eliminating any problems with the nut. If you've reduced fret buzz with the old strings that you've now put on then I suspect they're of lower tension (than the original set) so the neck now has less relief.

Fret buzz that high up is usually a sign of too much neck relief. If you like a really low action you might be better trying for a flatter fretboard/less relief.

I can't see having only two strings on it helping any with a twisted neck problem; if it was mine I'd remove the remaining strings and see how it responds.

That'll be just their normal quality control procedure before they get sent out surely? 😏