2006 Subaru WRX Creaking Noise

My Subaru makes a creaking noise (seemingly coming from near the pedals, maybe the firewall) under acceleration from a stop and under light to moderate braking. Also, sometimes during a pretty hard turn, but way quieter. I know it's not a problem with my brakes, because I just installed new pads and inspected the system. Plus, that wouldn't really explain the noise during acceleration. It just seems that with front/rear weight transfer, I hear the noise. Nothing going over speed bumps or pot holes, so I doubt it's the suspension. I had some transmission work done about 15,000 miles ago, so they had to remove the motor. Could this just be something not being tightened enough during reassembly? Please help me out, thanks.