There are no explicit "parking" sensors (it's not going to beep if you're about to back into something) but all but the base model have blind spot and reverse c

There are no explicit "parking" sensors (it's not going to beep if you're about to back into something) but all but the base model have blind spot and reverse cross-traffic sensors. I can't find any explicit mention of the trim from OP. It's quite possible he's incorrect in saying he has no sensors. I have a 2016 WRX with what should be the same exhaust. When you start the car, it starts with a high 2000-2200RPM idle and drops from there. If it needs to warm up, it will sit around ~1800rpm which is exactly where the stock exhaust makes the loudest drone. So simply starting the car and letting it idle should result in it hitting all the revs that trying to reverse would (unless OP is awful at driving stick and way overrevving it here). I find it way more likely there's a sensor interference issue than it's an exhaust issue based on the other information. My second guess would be some IR from the halogen running lights / fog lights / other lights in the car interfering with a motion sensor.