Bass buzzing at one fret!?

Do you have a fret that is proud of the rest?

Sometimes you have to reseat them.

 

Yep, check the fourth fret. Sounds like it got loose on ya.

 

I agree, it sounds like the 4th fet has popped up.

 

This is my process for checking a buzz on a single fret. It's important to distinguish between a loose, popped up fret vs a fret that's seated solid but too high, since they need different fixes. If you have a loose fret and you try to file it level, you can end up making the problem worse - when you try to file a loose fret to bring it level, the file pushes it down as it cuts (sometimes only partially), but then the fret will often pop back up after you lift the file off - so the fret will appear to have been leveled, but it's still too high and causing a buzz on the next fret out - so you didn't even fix the problem - and it may even now be too low when you're fretting the loose fret (since fretting on it will push it back down).

1) Get a short straightedge that only spans three frets. Move up the fretboard one fret at a time, checking to see if it rocks on any set of three frets. If you get a rock, the center fret is the one that's high. Be careful to not apply a lot of pressure as you check - you want to avoid pushing a loose fret downwards as you check since that can hide the problem or cause you to identify the wrong fret.

2) Get a thin feeler gauge (I just use the thinnest in my set). Try to slide it under the crown, i.e. between the fret and the fretboard. If it slides in, you have a fret that's popped up. If it does not, you have a high fret and it needs to be filed level (which can sometimes be done with just a few swipes from a crowning file, if it is truly just a single fret, versus leveling the whole fretboard).

3) If the feeler slides in, Put a spring clamp on the fret pushing it down into the fretboard, and check with the feeler again. If it does not slide in, the spring clamp has pushed the fret back down. Wick a tiny drop of thin CA under the fret, let it sit for an hour or two, remove the clamp, and check again. If it stayed down, you're done. If it popped back up, repeat.

4) If the feeler still slides in even with the clamp on, the fret may have popped up, but it is just too stiff in the slot for the spring clamp to push it down. When this happens, I lay the neck on a padded brace and tap the fret in with a fret hammer, then check again. If it's seated, proceed as above: spring clamp to hold it still, wick in a drop of CA and move on. If it does not seat even when hammered, proceed with filing to bring it level - sometimes, a fret appears to be popped up (a feeler fits under the crown) but there's really something else going on, i.e. the slot isn't deep enough or some debris is in the slot and stopping the fret from being driven all the way in, or someone else has already glued it, but they glued it in a not-fully-seated position. This doesn't happen often but I've seen it on some cheaper new instruments. As long as the fret isn't moving, you can just file it level and move on.

5) For a popped fret, once the fret is in place and no longer moving, check again with the straightedge to make sure it's actually level. Sometimes a popped fret will go right back where it needs to be with the above fixes, other times it ends up a tiny bit high or low after the fix. If that happens, file things level.

6) And finally, if any filing has been done, touch up with a crowning file and polish to match the finish on the other frets.

In my experience, an instrument that has played fine for a long time and suddenly has a buzz only in one specific spot is almost always a loose fret, and clamping/gluing or hammering it back in is a quick and effective fix and usually doesn't require any filing or touch up. I had a guitar in my shop a few weeks ago with this issue, and the owner was there with my as I checked and fixed it by tapping the loose fret back in and gluing it in place. It took longer to restring and tune than it did to actually fix. He remarked at the irony of "hit it with a hammer" being the solution to a problem on a fine instrument.

 

Or one of the outer ones is low. Let's say fret 6 is low. When you span frets 4, 5 and 6, the rocker will rock on 5. And when you span 6, 7 and 8, it will rock on 7. You might think frets 5 and 7 are high, but in fact is that 6 is the problem, being low.