The A string doesn't look right

Devil#20

I don't know what's wrong with the A string on my guitar and it's a bit hard to describe, so bear with me. It's an Epiphone Les Paul Deluxe (not that that's relevant). The A string is ringing on the frets when I pluck it but the other strings aren't. Short answer is higher the string but I don't think that is the answer. When you pluck the strings they vibrate nicely in the plane of the guitar and the vibration decays gradually, linearly and predictively. However, the A string doesn't. It vibrates like it's tuned to an octave down like it's lower tension than it should be. It isn't. It's tuned correctly. When I pluck the A string the vibration is excessive and it looks like it's pulsing rather than decaying gradually. I'm fairly sure that its vibrating in other than the plane of the guitar so no wonder it's hitting the frets. What I think I'm seeing is a beat frequency superimposed on the string. Does that make any sense? I've pressed on the string behind the nut and that doesn't seem to alter this basic odd vibration any. Could it be a badly tempered string rather than something in the setup? WTF can it be?

dazzajl

It could be a problem in the string, they do happen. It could be the "rattle'o'matic bridge living up to type and working loose on the A string?

skay

Dud string? If this is a new occurrence, then change it and find out.

crunchman

It could well be a dodgy string.  I'd change the strings first.

Just check your bridge/saddle isn't tilted back as well.  I had one once where the string was catching on the saddle.

Funkfingers

In no particular order, check;
• that the hex nut on the machinehead is nipped up properly.
• for cracks in the nut slot.
• that the A string saddle is sitting correctly in the bridge.
• for breaks in the string wrap wire.
• for lifting frets.
• for curvature along the neck.

Have you gone down a string gauge? Say, from tens to nines?

ThePrettyDamned

A video would help diagnose I think. 

viz

Could it be something rattling to that frequency? Have you tried fret 5 on the E string?

ICBM

Sounds like a duff string to me.

The only other likely possibilities would be a weird overtone caused by the neck pickup being too close to the strings - although that would usually affect the E string more - or a resonance in something like the truss rod which could be very close in frequency to the string.

Try either lowering the neck pickup or retuning the string a semitone up or down and see if either thing makes it go away.

Devil#20

There's some good suggestions there so I'll have a go at some of them when I finish work tomorrow. Working from home so I'll bunk off early cos didn't finish till 8pm tonight. I pressed the string between the bridge saddle and the end stop and it seemed to be a lot better (though still rattling on a fret somewhere). The string vibration may seem not to beat because of what ICBM said because I've effectively changed the pitch of the string. I've only just read all the replies so there's some fairly easy checks to carry out before I take the strings off and start tapping frets to check if any loose. Unless the nut is cracked I won't touch that. I'll whip the strings off, black up the frets if they don't seem loose, and give them a very light rub over with the fret leveller bar, Tighten the tuners then see if there's anything amiss with the A string saddle as the likely culprit. If I can't see anything wrong with that then I'll restring it, set bridge radius and intonation. If I still have a problem I'll whizz the whole fucking lot in the bin. 

Devil#20

ThePrettyDamned said:

A video would help diagnose I think. 

The frame rate of the camera may not show it as it is though.