I'm really not sure this is the right place to ask, but it's as good as any... I play a Gibson Thunderbird through a Markbass Littlemark 250 Blackline, and a GK 112 or an Ampeg 410. I've been taking lessons for the first time in 4 years, and my teacher pointed out to me that my bass has a lot of nasty fluctuating overtones, specifically on the C (3rd fret, A string) and G (3rd fret, E string). It happens mostly when playing over the neck pickup, much less so on the bridge pickup. My teacher thoguht it was perhaps my effects that put my signal in anti-phase, but I thought I'd test all the elements in the equasion. I switched strings (d'Addario flats to EBS rounds), cabs, amp, 3 different cables (although I'm npt sure of their quality, I know they're not top-notch, but decent, though),... I don't want to EQ this out, because it seems to be a structural issue... Could this be my bass, the pick-ups perhaps? Or are overtones that normal, and is it my playing (the teacher has it too, so I doubt it)? Maybe I'm overly focues on this, now that I hear it? Any advice?