There are a number of things that can contribute to warbling, RealZap mentioned
pick-up height. Yes, I see this often enough.
The sound sample is more indicative of string buzz (not warbling) from the string nut slots,
if there are burrs or wearing in the slots. Fret buzz can also contribute. Both kinds of buzz
can become part of the signal and end up being processed like the rest of it, hence this
distorted dual-tone effect from being Alt Tuned with the main signal.
Intonation can be off enough to where a dual-tone appears.
On a couple of occasions, an 89F turn out to have the piezo lines in the wrong sequence.
An easy fix at the service center.
Typically, it's a matter of which string and how it manifests. It won't always be the same
every time, in every situation. It requires a service tech experienced with this product to
tease that out.
Is on all the strings or just a couple?
Every fret,... or just certain strings on certain frets?
Trying to do it yourself can leave you chasing your tail or chasing ghosts in the machine.
It's not our grandfather's arch-top Gibson anymore, with passive electronics. Need a service
tech (Line 6 authorized service) experienced with troubleshooting this product for that one.