I was cleaning my engine one day and I heard a pop on the right side of my engine in between the brake master cylinder and the driver side suspension hub. However, when I look to see what it was I didn't see any sparks or any smoke so I thought it was nothing. But the next day when I went to drive it I heard a slight pinging/knocking sound whenever I pressed the accelerator and I also didn't have the power as before. So I took it to a mechanic and he said that it sounds likes a rod or wrist pin going out, but he was puzzled at how extremely quite it was at idle. Also whenever I first crank the car it runs without the noise but the longer I drive it the noise comes back. I believe that I could have popped a sensor or something because if it was a rod or wrist pin wouldn't it make the noise all the time but I'm not for sure. I've read that a knock sensor could cause the same thing. Any information would be greatly appreciated.