rattling/knocking noise
bigshot82
10-28-2008, 12:06 PM
car makes a rattling noise at about 40mph... gets faster with speed (not rpm) until it fades away in engine noise.
only when accelerating with a steady gas. (let go of the gas pedal... noise is gone)
no noise when idle.
no noise when running on the lift.
mazda protege 2001 standard transmission
only when accelerating with a steady gas. (let go of the gas pedal... noise is gone)
no noise when idle.
no noise when running on the lift.
mazda protege 2001 standard transmission
MagicRat
10-29-2008, 08:25 AM
Diagnosing noises without actually hearing it is tough. Let's start with the cheap-to-fix possibilities:
This might be detonation (ping). Here is the Wikipedia explanation:
Knocking (also called knock, detonation or spark knock, pinking in UK English or pinging in US English) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise time in the piston's stroke cycle. The peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. It should not be confused with pre-ignition (or preignition), as they are two separate events.
Try running a couple of tanks of premium fuel and see if it goes away. If it does, there may be something wrong with your car's knock sensor.
If it does not go away, there may be something loose on the car such as a loose heat shield for the catalytic converter, loose baffles in the muffler, loose clamp etc.
If these suggestions do not work, there may be something loose inside the engine, such as excessive piston clearance, loose wrist pin, etc. Fixing these problems is expensive so try to eliminate the cheap-to-fix problems first.
This might be detonation (ping). Here is the Wikipedia explanation:
Knocking (also called knock, detonation or spark knock, pinking in UK English or pinging in US English) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise time in the piston's stroke cycle. The peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. It should not be confused with pre-ignition (or preignition), as they are two separate events.
Try running a couple of tanks of premium fuel and see if it goes away. If it does, there may be something wrong with your car's knock sensor.
If it does not go away, there may be something loose on the car such as a loose heat shield for the catalytic converter, loose baffles in the muffler, loose clamp etc.
If these suggestions do not work, there may be something loose inside the engine, such as excessive piston clearance, loose wrist pin, etc. Fixing these problems is expensive so try to eliminate the cheap-to-fix problems first.
bigshot82
10-29-2008, 09:28 AM
already tried those. as I said, noise gets faster with speed, not RPM. so it is not the engine.
shorod
10-29-2008, 12:16 PM
Is there any vibration that seems associated with this rattle? Is it definitely a rattle, or could it be considered a chirp, maybe from a failing throwout bearing?
-Rod
-Rod
MagicRat
10-29-2008, 02:50 PM
it is not the engine.
Well, say so at the beginning! :)
That simplifies it a lot.
I would say CV joint(s).
Well, say so at the beginning! :)
That simplifies it a lot.
I would say CV joint(s).
Automotive Network, Inc., Copyright ©2026