[swimmingly]

I recently did a top engine refresh (didn't touch the head at all) and it seemed like all went fine. The car feels faster and has better response. I also just replaced the sway bars with 968 m030s and installed delrin bushings. For what it's worth, I also took it to an automated car wash place for an exterior cleaning.

However, today I picked up a loud low-pitch knock when the car is at idle. When the rpms are greater than 1200, the knock goes away. When I return to idle at a stop light or before parking, the sound returns.

My fear is that it's rod bearing failure, but from what I read, I think that would have constant knocking throughout the rpm range. Second, I'm thinking it's bad motor mounts. My car shook a lot before at idle and it went away at 1200 rpms, but I've never had this sound before. Could stiffening the suspension (bigger sways/delrin bushings) or even a car wash aggravate the crappiness of my old motor mounts? Any other ideas?