Technical Question For Luthiers

That sounds like a fret wear problem. Look close at the 5th and 6th frets under the G string. You probably have a slight wear groove, under the G string in its normal position. When you shift the string to the side and fret at the 5th, it's probably just touching the 6th, which deadens it.

If that's it, the fix is a routine fret leveling.

 

It's either fret wear, or magnet pull from the string being offset. Your bass probably has a little bit of a dead spot there going in. Don't sweat it - all Fender J & P basses have a dead spot between the 5th and 8th fret on the G string. When you have the string where it was, it probably lines up better between the pole pieces of the pickup, and there is less pull on the string. Moving it over puts the string more over a single pole piece, and that magnet can pull the string dead. It's most common on Strats, and it is called, "Stratitis." Lower the G side of each pickup a quarter turn to see if that helps.

Divots on frets can be funny things. Up close to the nut, it doesn't measure out any significant difference, but by the fifth or sixth fret, by moving the string, you may have put the string over a place in the fret with lesser wear, which will be taller compared to the lower frets, and it may be just slightly contacting the string and damping it. But it won't necessarily sound like fret rattle.

Also try raising the string at the bridge ever so slightly to see if that helps. The break angle over the G saddle is very shallow compared to the other strings, and that can affect sustain as well.

Finally, when all that is done, if you still lose sustain on that note, raise the string a tad more and tweak the truss rod about 1/4 turn tighter to see if that helps by effectively making the neck just a little stiffer, which changes the resonance that causes the dead note, but not so much it alters the relief noticeably.

I solved the playability problem by simply narrowing the entire string spacing and the neck heel width, and putting a neck version of the UltraJazz in the bridge (DiMarzio winds both the neck and bridge version the same; the only difference is the polepiece spacing, neck narrower, of course) and re-aligned all the strings on my custom half-fanned P/J. It has its dead note at 8th fret Eb on the G string. I'm just glad it's not worse than it is.

http://www.talkbass.com/threads/a-different-custom-p-style-bass.755914/