Alien buzz when using capo

[tremolo arm]

I recently discovered a very strange string buzz on my b string playing Tracy Chapman's Fast Car.
The song needs a capo at the 2nd fret.

The buzz is on the 10th fret of the b string, but here is the strange thing - it only buzzes when the capo is fitted and only when the capo is on the 2nd fret.

That means that it doesn't buzz on the 10th fret (or anywhere for that matter) when the capo is not fitted and it doesn't buzz if the capo is fitted on any other fret.

Here is a video I took to describe the issue: https://youtu.be/buSYPEX3RWA

Having the capo on the 2nd fret, there is no reason why the capo should be a factor when the note is fretted on the 10th fret, but to make sure I used two different capos and it's all the same - buzz on the 10th fret of the b, only when the capo is on the 2nd fret.

I've checked the bridge saddle and it's fine.

Any clues on why this could be occurring and any guesses as to how to eliminate it?

[TheWeaz]

Is it possible that the buzz is coming from between the capo and the 10th fret? What happens if, when capoed, you fret the 10th with your 3rd finger while damping the string between your 3rd and the capo with your 1st?

[TheWeaz]

Also, although you hear it when playing the 2nd string, are you sure that's where the buzz is coming from? Could it be another string making a sympathetic buzz?

[tremolo arm]

Yes, I’ve checked all these points. Definitely nothing between the capo and the 10th fret and the adjacent strings are solid too.

I think it might be something inside the body which vibrates at that frequency. But why only when capo’d and why only when the capo is on the 2nd fret and not happening on other frets? Very weird indeed...

Could it be that the cables inside have detached from the body?

[TheWeaz]

It's the "only when capoed at 2nd" that gets me. If a cable were loose, how would it know?
You say you "checked all these points" ... hate to pick nits, but how did you check. I'm guessing that you would have to play the offending note and mute each of the other strings one at a time.
Might it be behind the capo?

[timfitz63]

... I think it might be something inside the body which vibrates at that frequency. But why only when capo’d and why only when the capo is on the 2nd fret and not happening on other frets? Very weird indeed...

Could it be that the cables inside have detached from the body?

Sympathetic vibrations are curious things; they can be buggers to track down.  But I think you may be correct:  something inside the guitar body is resonating.  I have a 2008 T5 that had an odd buzz when plucking a certain string (don't recall which one now) fretted in a certain position (don't remember which now) when I first got it; I traced it to the battery compartment door, and fixed it by putting some extra foam padding on the back of the door so it remained damped against the battery.

As far as why it's only happening when the capo is installed on the second fret:  I'm guessing it's because the extra mass of the capo in that particular spot on the guitar drives the resonance.  On a lark you might try a different capo (i.e., one that's bigger/heavier) and see if that clears up the problem.  If nothing else, it would indicate whether my analysis is accurate...

[tremolo arm]

It's the "only when capoed at 2nd" that gets me. If a cable were loose, how would it know?
You say you "checked all these points" ... hate to pick nits, but how did you check. I'm guessing that you would have to play the offending note and mute each of the other strings one at a time.
Might it be behind the capo?

You're absolutely right to pick nits. And yes, I played the offending A on the 10th fret by muting all other strings and also by fretting adjacent frets behind the A (9th, 8th, 7th) at the same time.

Interestingly, the offending A seems to be triggered if played together with the F# - 9th fret on the 5th string. In other words, the offending A on the 10th does not typically start buzzing, unless it is 'instigated' by the lower note. It is so, so strange...

 

[tremolo arm]

... I think it might be something inside the body which vibrates at that frequency. But why only when capo’d and why only when the capo is on the 2nd fret and not happening on other frets? Very weird indeed...

Could it be that the cables inside have detached from the body?

On a lark you might try a different capo (i.e., one that's bigger/heavier) and see if that clears up the problem.  If nothing else, it would indicate whether my analysis is accurate...

Yes, checked with a different capo (different brand and design). Same exact thing. The guitar must be possessed!
Good job I don't use capos a lot. It's only on Fast Car and Camila Cabello's 'HAVANA' that the capo is on the 2nd fret. Must ask our singer to sing 1/2 a step higher...

[timfitz63]

... I think it might be something inside the body which vibrates at that frequency. But why only when capo’d and why only when the capo is on the 2nd fret and not happening on other frets? Very weird indeed...

Could it be that the cables inside have detached from the body?

On a lark you might try a different capo (i.e., one that's bigger/heavier) and see if that clears up the problem.  If nothing else, it would indicate whether my analysis is accurate...

Yes, checked with a different capo (different brand and design). Same exact thing. The guitar must be possessed!
Good job I don't use capos a lot. It's only on Fast Car and Camila Cabello's 'HAVANA' that the capo is on the 2nd fret. Must ask our singer to sing 1/2 a step higher...

Well, kind-of throws that theory out the window...

Double check everything that's supposed to be tight (e.g., tuner posts) are tight.  Try taking out the battery holder, just to see if that's the culprit.  If you haven't tried changing the string(s), that might be worth a try too.  Also inspect the fretboard in the location where the capo gets installed, as well as the second fret itself, for excessive wear or warping; if that string isn't being fully held against the second fret, plucking the string at the 10th fret may cause the string to resonate between the capo and the nut.  To test this theory, wrap a rag or handkerchief around the first fret so that none of the strings can resonate behind the capo.

Yeah, I'm probably reaching now, but you're rapidly getting to the point where your only option will be to sprinkling holy water on the guitar/capo...