String height problem

[Johnozouk]

My SOS mandolin has developed an odd problem. After years of flawless performance, the E string is acting strangely. When I fret the E string at the 7th, 8th, and 9th frets, the string seems to be hitting other frets and the note is muted. This does not happen anywhere else on any string. If I fret the E at the 6th fret and below, the tone is nice and clear. If I fret the E at the 10th fret or above the tone is nice and clear. I had new frets installed several years ago, and there has been no problem until now. I replaced the strings, and the problem did not change.

[HoGo]

Sounds like you have pretty standard setup issue.
Could be few worn frets, or one loose fret end up the neck or neck relief needs to be checked...
Several other possibilities as well.
You should visit good mandolin luthier and he'll tell you in a minute what's up.

[pops1]

Sounds like fret 10 has lifted slightly and needs a tap down. It is common this time of year for frets to lift.

[Greg Mirken]

The fact that the phenomenon occurs on the E strings, near the fingerboard edge, supports the loose fret theory. I check for loose fret ends by tapping a steel 6" rule on each fret end. A tight fret produces a clear "tink" and a loose fret end gives a dull "thunk". The remedy is either tap it down and hope it stays, or wick a droplet of thin CA under the fret and hold it down til the glue kicks.