2012 991.1 same issue as we are all having. A very annoying styrofoam sounding squeak that sounds like it is being emitted from under the dash area. My sound was indifferent to tank fuel level, just horrid.
Fix? I popped off the cowl in the frunk and went to town with a can of silicone spray, hit everywhere my hand/can could reach focusing on the firewall area. Some spots I could not hit directly so sprayed a ton of lube along the firewall and let it seep down. Silicone spray is great in that sense, it doesn't leave a dripping mess that other more popular lubes like WD40 possibly would. I also sprayed the upper strut mounts and let it seep in good and proper.
Drove it 30 mins later and the squeaking has gone, so it was either or my upper strut mounts or the tank pads. Whatever it was, happy have it gone.
This thread was incredibly helpful to say the least, thank you fellow R-listers....