Can anyone tell if my car is detonating? Lately I've noticed that the car is making weird noises when I'm driving on the highway (usually around 60 mph). It sounds like something is rattling/grinding. It doesn't always happen on the highway, only sometimes (seems to be triggered by slight bumps on the road). Once it noise starts happening, it goes on for a few minutes. I can never get the sound to happen during around the city though. The noise sounds like it's coming from somewhere between the back of the motor to the cat. converter.

I even gave the car more gas on the highway when I got the noise to happen to see if gets louder but I can't really hear it over my exhaust and SC. So if it's detonating, wouldn't it get louder as the RPM increases? Car is driving fine and no CEL is on.