Posted this in 3G Wheels & Tires but just wondering if anyone here could lead me in the right direction...

Heres the story....I was coming out of my friends neighborhood, and I took a back way home. I didn't realize there was such a big dip in the road and pretty much bottom'd out. It felt like I hit the actual subframe, and not the air dam/front lip like I usually do because it felt really bad. Got out of the car, looked around...no physical damage that I could see. Couple hours later (or maybe it happened right away) I noticed kind of a rattling sound when i lightly tap the accell....sounds really wierd....metal rattling is the only way i can describe it. It only happens when i'm in motion and the wheels are spinning. It seems to get more pronounced the harder I hit the gas. Its pretty faint, and you can only hear it when all the windows are up and the radio is off...

Cliffnotes...
Its intermittent (part of last night, it didn't do it at all)
When it does happen, it *ONLY* happens in Drive & at low speeds (5-10mph)
Only happens when you initially hit the throttle, or give it a jolt
Sounds like metal rattling (spinning motion)


The thing is, if it was a drive axle, which I originally thought, wouldn't it constantly be making a sound regardless of speed? Also, wouldn't it be much more noticable than a sound...like harsh vibration or really clunky feeling?
Any ideas?

 

 

No clue about your noise. Typically when drive axles make noise it's at lower speeds, at higher speeds torque forces all the pieces to remain packed together. Also when a CV joint is making noise its very violent, loud cracks, creaks and metal on metal noises.

 

Yeah, I remember that from my Legend... The CV joint went out, and man...everyone within a 10 mile radius could hear me turning. Its much more faint than that...in fact, if the radio is slightly cranked you can't even hear it. Its deff not something you can feel either...

 

The only metal on metal noises I've heard from my car is the catalytic converter heatshield. Have a look under the car and have somebody tap the gas, or wait until it cools down and climb underneath and see if there are any loose heat sheilds. They are only spot welded on to the pipe itself so if the impact was hard enough to knock one loose, that could be it...

 

I had a Civic that got a small rock under the shield and it rattled at certain frequencies.

 

Thats what I was thinking, but then it would do it in park right? Seems like it only makes the sound when the wheels start spinning...I can rev the engine in park and it wont make the sound, but i'll double check.

 

might be the bearings
throw the car in neutral while driving and see if the noise disappears

 

Thats not a bad idea but the sound only happens when i tap the gas pedal...once i release the throttle the sound goes away, i'll try that though...see if it does it in neutral

 

Not sure if the TL has metal exhaust hangers, but if it does its possible one is bent and moving around. Another possibility is a bent heat sheild making noise. You really need to get a look under the car and see whats going on.

A bad bearing would make noise if the car is moving, no matter if your on the gas or not.

 

a bearing would only make noise when accelerating... it will start making noises while just cruising if your hub also goes

 

bearings will make noise no matter what if you were moving

 

most likely the heat shield. i probably only rattles when the engine is under load.

 

As other have mentioned, you may have loosened a heat shield, or bent/damaged the exhaust system. The exhaust system is on hangers or rubber isolators, and you may have bent something when you bottomed out.

It may be more prevalent during the conditions you have listed as the engine is under load during acceleration. Remember the engine is not solidly mounted to the frame, but is on pliable (flexible) mounts instead. You mentioned it only happens in Drive and at low speeds, which I assume to be accelerating. The entire powertrain would be shifting somewhat under these conditions, and if the tolerances between the exhaust and heat shields is compromised in some way, you may indeed hear a rattling sound. If you take the car to a wide open parking lot, accelerate to 10 mph and in Drive and turn off the ignition. You probably won't hear the rattling sound if this is indeed the problem as your powertrain isn't under load and moving on its mounts. During this test you won't hurt the car, but be prepared for your power steering and brakes not to function properly.


Terry

 

Ok cool, i'm gonna go to my friends place and put it on the lift, i'll inspect the entire exhaust system and the surround heatshields....thanks guys

 

On my Taurus it would only do it when I wasn't pushing the clutch. If I had the clutch in it was silent, take it off and it would start to rattle... We started thinking throw out bearing, luckily it was a much cheaper fix...

 

He can fix that with gauze pads and Quaker State.

 

If it happens when you accelerate, it can very well be the exhaust hangers, cat heat shield. Bearings will make noise only on the side in which you're turning ie. turn right, sound comes from the right side.

Another culprit, albeit not that likely, is a brake dust shield. If it has come loose, that might make the noise.