I've had the same Full Circle on my 60s Kay for a while. I'm guessing it's been at least eight years, though I don't play nearly as much upright as electric bass. From reading Talkbass threads, it seems like they have a shelf life. I just noticed that the 'E' an octave up from low E is distorting. It doesn't matter if I play it at the 2nd 'fret' on the D string or the 7th on the A string- same story. I tried switching instrument cables, detaching and reattaching the RCA plug from the pickup to the jack, etc. My action is on the high, bluegrass side. I have the adjusters almost all the way down, though there is a gap. I think the bass would be unplayable otherwise. Is this evidence of the pickup going out? Or, would the effect occurring only on one note suggest something else? eg would it happen more uniformly across the range of the instrument if it were the pickup? Acoustically, the bass sounds fine at that note. I perused some previous posts but did not see this specific problem. Any help is appreciated. It seems like repair through Fishman is an option, and in these Covid days, a couple weeks without a pickup is okay. Tangentially related: if anyone has good luck with a pickup on an old Kay (or similar plywood bass), I'm open to try something new. I'm using D'addario Zyex strings and getting a nice tone. Not going for a super-stringy sound, but a singing mid range and some sustain is always welcome.