what cause the rumbling noise in the exhaust when I lift the throttle from above 3000 rpm?
Ray. Gonna need a little more description than "Rumbling sound" Is it a burble? You know, the blub, blub sound lots of cars make when they decelerate? Is it a pop, pop, pop? Almost like a backfire? kind of loud? Is it a loud 357 magnum style bang noise? You know, an old fashioned backfire. Is it a vibration that can be felt in the car? Does it go away at some point as the rpms decline, but before idle? Can you make it go away by applying very slight throttle while slowing down? Not enough to make the car accelerate, just enough to keep the car from making the noise. Details will help with the diagnosis.
It's normal. You can tune some of it out of the system, but it's pretty much normal for them to do some burbling on deceleration. Also, it may be your exhaust system. Do you have a stock Dino exhaust? The exhaust can make the problem worse if it doesn't follow the original air flow pattern.
