I just had this squeak develop right after my 3yr warranty expired, go figure! I thought it was a suspension thing at first since i only heard it over bumps, but found it yesterday sitting in my car, stopped, that i could create the noise. My issue seems to be coming from the right bolster as you sit in the seat. I saw you mentioned your lumbar cable being the culprit and I'm wondering if that's my issue. I use the lumbar button a good bit so I'll try that.
The dealer thought the noise was coming from my overhead compartment in front of the sunroof, so they charged me $25 to put some anti-friction tape in there. I just emailed them to let them know the real issue so perhaps they'll bring me in to fix it for free, otherwise, I'll go the DIY route.