It shouldn't have anything to do with the RAM in my humble opinion. It sounds to me that it might be the way you are routing your outputs. Are you outputing to a Mixer then to Speakers?? Or directly to Speakers from FG outputs?? Also, Main Outputs A (MIX) outputs the whole signal, while Outputs B do not output everything from what I understand. Although what outputs you are using shouldn't be the cause of the distortion but what you are hooking them into e.g. Amp, then to Mixer, then to speakers, or directly to Speakers, etc. could, depending how your outboard gear i.e. (Mixer, Patch Cables, Amp, etc.) are setup. Did you check your Audio Cables to make sure they are okay? You don't have a Mic on with the volume up when it happens do you?? :0 Are you routing the signal to a Sound Module and/or to a Computer too perhaps? If you are using MIDI Output and Input on the Fantom G make sure it is setup correctly on the Fantom G and on your external gear. Does this happen only when you play the keys or does it happen when you play an SMF, Audio, or Phrase too? You don't have anything connected to the INPUTS on the Fantom G with the Input Level knob turned way up do you?? Have you tried resetting the Controllers by pressing the Shift then Single Mode button? Did you happen to increase the Output Gain signal in the System Menu/Sound tab? Increasing it too much can affect the output signal significantly, causing distortion. Hope this helps. And that you get it figured out and fixed soon.
PS: It sounds like it's something that you aren't doing right i.e. some setting(s) that are set incorrectly on the Fantom G or on your external gear etc., or possibly the way the signal is routed, or how your patch cables are patched together and/or what they're patched to. Or possibly something in the System Menu not set correctly, etc.. But I really doubt it's a defective Fantom G in my opinion. Of course I could be wrong about that but my gut feeling is that it's not a bad FG but something you did (or didn't do) that has caused it.

I'm not trying to blame you or anything like that. I just find it hard to believe that a brand new Fantom G6 just suddenly goes bad. Roland's quality control is better than that in my opinion. And if it's something to do with the OS i.e. a "bug" or something of that nature, then everyone of us who has update 1.10 installed on their Fantom G should be experiencing the same malady.

Which we're not thankfully.

Again, I'm sorry for the unfortunate situation you are having with your FG. If it's truly a defective Fantom G then Roland should take care of you and it should be resolved promptly, no questions asked.