[dolph]

Did you ever find the cause of this?

I'm having this exact same issue, although I have a stock tune and an almost entirely stock 2013 BRZ Limited auto (save for a K&N drop in filter). The car has never been to the dealer for any reason (no recalls, etc). I had the chirping issue for 3-20k miles or so. Currently at 33k miles.

My car has thrown this code twice. On both occasions, the sequence of events has been as follows:

1. Low fuel light comes on, as expected, during normal driving. Fuel gauge seems steady and accurate. I legitimately need gas.

2. I'll get to my original destination, thinking that I'll get gas afterwords. I'll park the car for over an hour.

3. Car seems to struggle a tiny bit to start, almost like the battery not fully charged.

4. Shortly or immediately after starting the car, the CEL will come on. I'm not sure when it comes on because I might just not be noticing it immediately, due to the other orange lights already on my dashboard (low fuel, etc). Car runs fine, otherwise.

5. I'll stop for fuel, turn the car off, fill the tank, check and clear the CEL. P0463.

6. Again, the car seems to struggle a tiny bit to start, almost like the battery not fully charged.

7. Many driving cycles follow without a Low Fuel light, without any noticeable trouble starting, without any unexpected fuel behavior from the fuel gauge, and without a CEL.

Perhaps coincidentally, this has happened on two consecutive tanks of gas from different gas station brands in different parts of town.