Assuming the ECU update is free, I would do that first. Just tell the dealer that's the only thing you want. If it solves your troubles, then you are done.
You didn't happen to install any new audio equipment did you? I've had mounting screws go right into the wiring harness.
2002 Black SE-R 5 speed.
Nismo I, WRP IM Spacer, OBX H, XS Power C/B
Motegi LC5 17x8 with 235/40/17 Falken Azenis RT-615, Tien SS, Eibach Sway bars, Nismo Lower Tie Bar, Specless Trunk Bar
Waiting to go on: WRP U/D Crank Pulley, WRP Throttle Spacer, WRP U/D Steering Pulley