I had the same exact issue on my 2016 GT350 - sounded like George Jetson's space craft when I started driving and couldn't eliminate it no matter what we did.
I ended up with just replacing the factory speakers, kept the LC6i sound processor and 500w mono amp for the sup. Sounds better but the factory head unit doesn't drive the Kappa 100w coaxial speakers. Pretty disappointing.
According to some experts I talked to there is nothing that can be done (for now) short of replacing the head using.. which I'm not going to do.
I ended up with just replacing the factory speakers, kept the LC6i sound processor and 500w mono amp for the sup. Sounds better but the factory head unit doesn't drive the Kappa 100w coaxial speakers. Pretty disappointing.
According to some experts I talked to there is nothing that can be done (for now) short of replacing the head using.. which I'm not going to do.