I always set up my own basses, and luckily none have ever needed anything more than a tweak and patience. So, i know the basics of set up but not sure what to look for in this case. My Fender Sandblasted P bass has been perfect for the past couple of years, never had any issue and its one of the best necks ive ever played. Over the past month or so ive been noticing a really loud string rattle/buzz when playing Bb on the E string. It moves fret position if i down tune the string, but comes back when its tuned to standard pitch. Ive gone through 3 new packs of different strings, all with the same result. Playing the E open doesn’t produce anything out of the ordinary, and no other string has this issue. I always set my basses up to the Fender recommended spec, as this just seems to suit my playing. Neck relief and action are as i want them, and this set up is the same on all my basses. The problem i cant fathom is if i place a cloth (T-shirt, micro fibre cloth etc) behind where I’m fretting it kills the buzz. Can anyone advise what’s happening? Do i maybe have a low fret that needs fixing? Ive run a steel ruler and used a feeler gauge over the frets and to my eyes all looks fine. Luckily with pick playing its not so bad, so its still usable, but annoying none the less.