My 15 STI was making a horrible knocking sound when off power/coasting. It was coming from the driver side front. The higher the speed, the louder it was.
It sounded like something that was spinning. After narrowing down the conditions to make the noise happen, I assumed it was a CV axle. I had it towed home to be safe.
I got it up on jackstands, removed the front wheels, and began to look for possible causes. Ball joints, sway bar end links, coilovers. Everything looked good. The CV Axles even looked good.
While I was under the car, I serviced the front trans/diff. Fluid looked good. Minimal metal debris on the plug. Filled with Motul gear oil.
Got the everything cleaned up, wheels on, and tools put away. Took it for a drive to circulate the fluids, and replicate the terrible sound. Heard nothing. Drove it up to highway speeds. Let off the gas to coast. Heard nothing. The condition that caused me to tow it home, was gone. This blew my mind. The sound was horrible, and potentially dangerous. No way a trans service would fix the sound.
I’d like to hear if anyone has had this happen to their STI. Any wild ideas to what happened?