Buzzing only when fretting 5th fret on the low B, or....
 

...when fretting the 5th on the low B but plucking the octave E at the 7th on the A string. Buzzing sounds to be coming from around the 3rd - 5th fret on the B string only (even when sounding the octave). The neck has a tiny bit of relief (typical set-up). The action is not super low.


Thoughts and/or advice?

Thanks

I would check for anything loose anywhere on the bass. Try "thumping" the bass with your fist and listen for anything buzzing or rattling. I would also tighten the truss rod about 1/8th turn. Just enough to make sure it's not rattling/buzzing.

When you play the note, mute the string between the fret and the headstock. If it stops the buzz, it is likely the string hitting the frets because the slot in the nut on the B string is too low. I have this issue on a jazz bass, I slotted the nut deeper on all strings because the flatwounds I used at the time were way too high at the first fret. When I put the roundwounds back on, I had this rattle on all strings. If muting the string silences the rattle, loosen the string and put a small piece of tape in the B string nut slot and replace and retune. If that is not enough, try a second piece of tape. It is a temporary fix, but it lets you know what the problem is.

Put a capo on the first fret. All buzzing has stopped. Hmmm...just bought this bass last night. Guess its going back for either a new nut, or an exchange.

Thanks