So my Max makes a knocking noise, Its only when the RPM's are dropping and its only at low rpm. when I upshift in a low gear or when I turn the car off it makes this noise. its always under 2000 rpm. It sounds like its coming from the motor, ive heard it with the hood open it sounds like valves knocking or rattling. There's never a noise when the rpms are rising just dropping. My car has 117K on it, I run only 93 octane fuel, and theres no other signs of anything wrong with my motor, no hesiatation, idles fine, no other noises. Any help would be greatly appreciated. Tried searching but couldnt really find what I was looking for. Thanks.

 

Sound like engine ping/knock usually caused by running low grade gas, you should be using 91 octane. You can also have a build up of carbon deposits. I to have a small degree of engine ping around 1800-2000 rpm when the engine is very hot. I am able to make it go away by using 94 octane.

 

i had this problem...it was actually my rear header...the cat inside came loose and was rattling lik a **** when de-accelerating ... this is a rare problem that many people dont kno about...i found out the problem when i replaced my headers with aftermarket and shook the cat and it actually was loose and was moving up and down...deff get it checkd out