Weird Little "Boink" after Truss Rod Adjustment?

[Googster]

Hey, All:

I bought a 2013 Martin HD-28 a little over a year ago and I fell right in love with it--it's a great player. From the get-go, my only complaint was that the action was a bit high from the fifth or seventh fret on up: not terrible, but clunky enough to slow me down some. The 28 came with light-gauge strings. I prefer mediums, but considering the slightly high action, I've just kept on using lights.

Well, I recently switched over to mediums and, as you might guess, the action got a bit stiffer. I figured it was time to measure the relief and give the truss rod a turn if needed.

The relief at the 8th was definitely above Stewmac's recs, so I gave the rod a couple little tweaks, totaling maybe 3/16ths of a turn, tops. This lowered the action just a hair and I was delighted. Though still a tad high, it's much, much more comfortable.

Okay. PROBLEM:

Plays great, sounds great EXCEPT: There's an odd little...what?...rattle? No, it's more like a little tonal "boink". It's all over the fingerboard. When I tap the G at the 5th, for instance, it makes a little, high-pitched "boink" (It's actually a rattly little A-flat) and I hear this "boink" simultaneously with the fretted C note. When I tap at the 6th fret, the "boink" lowers in pitch to a very high G that you hear simultaneously with the fretted C#.

As I say, It's all over the guitar, but most pronounced on the middle strings. It's as if the guitar is playing the front of the string and the back of the string at the same time. If you fret exactly at the microsecond that you pick, you don't hear it, but if your timing is just a hair off, you hear this rattly little "BOINK" clear as day.

What the heck IS that? More importantly, what can I do about it? Have I killed the goose that was laying all those golden eggs?

Any help, suggestions or feedback would be greatly appreciated. Thanks much!

[Rodger Knox]

I believe what you hear is the string contacting a higher fret than where it's fretted. It's usually just one or two frets above where it's fretted, but it can be more. There are lots of things that can cause a buzz or rattle, so I'll direct you to the place with all the answers, Frank Ford's site.
http://www.frets.com/FretsPages/Luth...buzzintro.html

[Frank Ford]

My quick guess is that you'd want to look at what we sometimes call a "back buzz," the sound the string makes between the nut and your fretting finger. Particularly when you hammer-on or tap the strings that can be more noticeable if you've reduced or eliminated neck relief.

I recommend a trip through the Buzz Diagnosis Pages at FRETS.COM

[Googster]

Thank you, Frank. Yes, I think that's precisely what it is, and I had already figured that out after Rodger was kind enough to refer me to your excellent page. Your description of my problem was right on the money. And while I cannot fathom the physics of why a low nut would make my guitar play two notes at a time (except maybe that the elves living in the wood are unhappy for some reason), the information you provided will be invaluable when I bring this problem to my local guy next week. Thanks again, gentlemen.