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Discussion Starter #1
I keep hearing this weird noise similar to CV joint when they start to go bad, but there is no CV joints in the front...the noise start after few seconds when cruising down, once I hit brakes or gas pedal noise goes away instantly. I lifted the car and checked the front suspension, lubricated all friction points of lower control arms, brake and sway bar links are good, wheels are tight, no wheel bearings play or noise.
Anyone had this issue before?
 

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Rust on the rotors? Shaking in the subframe? Bumps in the belly pan?

Could it be a resonance causing something to vibrate?
 

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...if it only happens in the first few yards of traveling ...let's say half a block...it is the ABS self check...and You can feel it on the brake pedal too..

Jetfuel...it is normal........me...debatable....
 

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Discussion Starter #4
Rust on the rotors? Shaking in the subframe? Bumps in the belly pan?

Could it be a resonance causing something to vibrate?
I removed the belly pan and noise still there, its like metal against metal sound clunk, clunk, clunk when cruising. I don't think rusted rotors will make that sound, my brake pads and rotors are good, I don't see any loose bolts on the sub-frame either.
 

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How about the brake heat shield? I’ve seen them dented and hitting the rotor or inside of the wheel.

Have you checked the brake pads? I’ve seen the pad become separated from the backing that might cause this, but it’s a long shot.
 

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Discussion Starter #6
...if it only happens in the first few yards of traveling ...let's say half a block...it is the ABS self check...and You can feel it on the brake pedal too..

Jetfuel...it is normal........me...debatable....
it happens whenever cruising in gears, any of these will make the noise goes away applying brakes, pushing accelerator, for example if I am coming to stop light, when I remove my foot from gas pedal to slow down the noise starts, once I push the brakes to stop it goes away or if traffic start moving and I push gas pedal the noise goes away and it is loud.
 

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Discussion Starter #8
How about the brake heat shield? I’ve seen them dented and hitting the rotor or inside of the wheel.

Have you checked the brake pads? I’ve seen the pad become separated from the backing that might cause this, but it’s a long shot.
I checked the brakes nothing wrong with them, when I lifted the car to spin the wheels manually I didn't hear any wheel bearing or backing plate sound.
 

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Hmmm, could it be a tire out of balance? Difficult to detect except at highway speeds.

Or... a stone or nail in the tire tread. It’s got to be something that’s rotating with the wheel.

Is there a little lip that’s formed on one of the brake rotors on the edge of where the pad sits (check both sides), where the pad has worn a groove into the rotor? If there is, it needs to be sanded off.
 

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One more thought - there is a small gap between the back of the bearing and the knuckle. The gap is only a few MM. the ABS sensor reads across the gap. It might be worth checking to make sure nothing got stuck in there.
 

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Discussion Starter #14
When I bought the car the front brakes looks like recently been replaced, tires also are new nd all wheels torqued down.
I replaced all 3 motor mounts not to get rid of the noise but because couple where worn out, I may have to record the sound and post it here.
 

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Discussion Starter #15
This a video I found on YouTube somewhat similar to the sound I am talking about, but not a Smart car.
 

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Strange noise under car

Do you have any mods to the car? If you have wheel spacers, make sure the lug nuts are tight.

You might also want to see if you have a buggered thread on your lug bolts and threads. If one was bad, it might not seat completely and may be preventing the tire from being tight.

Do you have stock lug bolts? There isn’t a lot of room behind the rotor for extra length to protrude. If the lugs screw in too far, the tire won’t even rotate. If just slightly too long, the tip of he lug will make contact with the bearing hardware .
 

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Discussion Starter #18
The only change to the car is replacing the front stock alloy wheels ( 15"x4.5" rim and 155/60R15 tire) with steel wheels ( 15"x5.5" rim and 175/55R15 tire), the steel wheel is from another smart car and I used my original bolts.
 

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Check the springs. One may have popped off the front support and be improperly seated and rubbing on the tire or rim.
 
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