The thing about this topic topic si that the string suddenly sounds bad. We have to think about what could cause a sudden change more than what cause strings to go false in general. It’s odd.
The bridge hasn’t come unglued locally at that position has it? Air under the bridge can potentially cause trouble, and glue can let go suddenly if not done right.
Which note is it? Is this a double pinned string?
Hi Chris,
Either I’ve missed a post , or may I suggest that the bridge or nut profile may now be at fault. If the string diametre is less than the previous ( Zuckermann original strings had rather large gauge jumps and Vogels’ WFE has very fine stepping; their brass too, so many really. Perhaps a little less possible but if the tension has increased to a larger diametre, in either case this might have led to yer string settling down more into the bridge or nut material. It’s point of depart is no longer the pin but the wood, this makes for an unacceptable tone colour. I’ve had a similar case on a homemade job where the maker had the profiles backwards. The strings left off on the wood, both ways. Maybe he was trying to make a keyed guitar, but it sounded most dull.
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I cant believe all the speculation in this thread, when we dont have all the facts or know what actual “bad” sound the owner is complaining about. Thrashing about in the darkness like this is not very helpful. What confidence would you have in a doctor who diagnosed your illness in this way, when all he knows is that you feel “sick” and he hasnt given you a thorough physical examination?
David
We are all trying to help but of course sight unseen it is difficult, and all the ideas are worth pursuing when @Chris415 gets to look at it.
I’ve seen bridges with local gaps; I’ve seen a harpsichord with the soundboard horribly cracked and warped which parted away from the bridge for many inches here and there - and I mean you could see through the gap - and all sounded fine. Mostly, soundboards act as a whole, or so I think is the consensus today. Local faults shouldn’t affect the local string.
A very good hypothesis! Only objection would be I can’t figure how the notch in the bridge wood could have been made “suddenly”. However Chris should definetly check the bridge/nut profile on that string.
Which is exactly what we get nowadays with telehealth, which has become the norm. 
Hi everybody,
First of all: thank you for all your suggestions, they are most welcome.
The annoying thing is that I don’t have easy access to the instrument. The owner is an artist who doesn’t indulge in modern technology. So forget about him making pictures/recordings with a smartphone (he doesn’t have one).
From you reactions, I think the most likely thing to investigate is indeed either the pins and/or the string touching wood before coming to the pin.
Probably this weekend or at latest next Tuesday evening, I’ll can lie my hands again on this instrument. In any case, if I find the culprit I’ll let you know.
Enjoy your weekend,
Chris.
But why should that happen “suddenly”?
WGK
Exactly what I pointed out earlier is the crux of the matter.
We eagerly await the in-person diagnosis.