Car is a '99 GT with 120k on it. Auto tranny.
The car since purchased, about 6mos ago, has a pretty loud rattling sound coming from what appears to be the center of the motor. It does it both when cold and when warmed-up. It only does it between 1500 and 3000k rpms. It will do it while moving, or at a dead standstill when just revving the motor.
It sounds like a metallic rattling coming from right in the middle of the motor. You can hear it from under the car, although it's not quite as loud. And it is equally loud from both sides of the motor, left and right. I've thought maybe it was something loose in one of the cats, I've I've considered some kind of pre-ignition. I've tried running 93 octane to no avail.
Oddly enough, when driving, you can hear it very clearly at part or neutral throttle, but as soon as you accelerate, the sound disappears. It is also absent under deceleration. Any suggestions would be greatly appreciated!
I'm running out of ideas. I've heard of some kind of intake cracking, but it sounds more like metallic rattling than plastic. Maybe an exhaust manifold crack somewhere?
Also, and this may be completely unrelated, if you rev the motor from the throttle body with your head under the hood, if you open the thottle sharply from idle, you can hear a "whoosh" intake sucking from somewhere toward the rear of the motor. It has a K&N intake, so that may just be normal intake noise, but it sounds like a substantial sucking sound. Again, may be completely unrelated.
The car since purchased, about 6mos ago, has a pretty loud rattling sound coming from what appears to be the center of the motor. It does it both when cold and when warmed-up. It only does it between 1500 and 3000k rpms. It will do it while moving, or at a dead standstill when just revving the motor.
It sounds like a metallic rattling coming from right in the middle of the motor. You can hear it from under the car, although it's not quite as loud. And it is equally loud from both sides of the motor, left and right. I've thought maybe it was something loose in one of the cats, I've I've considered some kind of pre-ignition. I've tried running 93 octane to no avail.
Oddly enough, when driving, you can hear it very clearly at part or neutral throttle, but as soon as you accelerate, the sound disappears. It is also absent under deceleration. Any suggestions would be greatly appreciated!
I'm running out of ideas. I've heard of some kind of intake cracking, but it sounds more like metallic rattling than plastic. Maybe an exhaust manifold crack somewhere?
Also, and this may be completely unrelated, if you rev the motor from the throttle body with your head under the hood, if you open the thottle sharply from idle, you can hear a "whoosh" intake sucking from somewhere toward the rear of the motor. It has a K&N intake, so that may just be normal intake noise, but it sounds like a substantial sucking sound. Again, may be completely unrelated.