The exhaust rattle you're getting with the EcoHitch Trailer Hitch Receiver # 306-X7257 in place on your Subaru WRX actually isn't too uncommon and there are a few simple ways to resolve this. We actually have a great article dedicated to exact this subject, which I have attached below.
The easiest solution is to simply bend the exhaust hanger a bit to provide more clearance between it and the hitch. You can just use a pair of vice grips or some pliers to manipulate the hangers so you... view full answer...
The Curt T-Connector Vehicle Wiring Harness # C56259 is designed to work with your 2021 Subaru WRX, but if you've had it that long and reinstalled it that many times I wonder if the wiring is just worn out. Here's what I recommend doing to determine if the issue is compatibility or just the wiring itself:
Connect all of the wiring as the instructions call for it, and then use a circuit tester to see if the correct signals are on the correct wires prior to the converter box. Then do the... view full answer...