Weird scraping noise

[lochs]

Hey guys, on the way home from the gym I experienced this weird 'scraping noise' as if a tin can was attached to the bottom of the car and dragging on the road, never heard this sound before. So I pull over, check underneath, nothing. Open the engine bay, looks normal to me, no engine lights on or anything. So I continue driving, and then the sound stops after about 4 minutes. Car is a 2016 s4, pretty much a base model, no sport diff. Only mod is an ecs tuning intake. Anyone got any ideas what's going on? Pretty odd noise to hear from a pretty much brand new car.

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[jygesq]

possible a rock caught in the brake shield. might have worked it way out.

[SteveYem]

Was it warm out, and was the sound coming from the rear passenger side?

[Reckon]

When you get a chance, try to get the car up and look around the wheels. Oddly enough, I had a wire coat hanger stuck in the undercarriage by the front passenger wheel and it would hit my wheel when I turned left. Didn't see it from underneath at first glance and kept getting this thud noise when turning left.

[lochs]

Was it warm out, and was the sound coming from the rear passenger side?

Yes it was quite warm, around 27 degree Celsius, and it did seem to come from the rear end of the car

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[SteveYem]

Yes it was quite warm, around 27 degree Celsius, and it did seem to come from the rear end of the car

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Yesterday and a couple times previously I heard a buzzing/rattling/vibrating/scraping sound coming from the rear passenger side. In all cases it was above 70F (20C) ambient. The sound is most prevalent when accelerating, but occasionally I would hear it while cruising or decelerating in gear. The sound does not happen constantly, but when it does happen it is a steady sound (if that makes any sense). When I heard it yesterday, it was only during one drive cycle, and it was only for the first 10-15 minutes of that drive cycle, then it went away. I also confirmed that I have nothing hanging from the bottom of the car or interfering with brakes and/or wheels.

I imagine the fuel pump is located back near the tank which is in the area from where the sound is emanating. I'm starting to think it is an issue with the fuel pump.

[lochs]

Yesterday and a couple times previously I heard a buzzing/rattling/vibrating/scraping sound coming from the rear passenger side. In all cases it was above 70F (20C) ambient. The sound is most prevalent when accelerating, but occasionally I would hear it while cruising or decelerating in gear. The sound does not happen constantly, but when it does happen it is a steady sound (if that makes any sense). When I heard it yesterday, it was only during one drive cycle, and it was only for the first 10-15 minutes of that drive cycle, then it went away. I also confirmed that I have nothing hanging from the bottom of the car or interfering with brakes and/or wheels.

I imagine the fuel pump is located back near the tank which is in the area from where the sound is emanating. I'm starting to think it is an issue with the fuel pump.

Interesting, do you have any ideas about what would be wrong with the fuel pump? I'm going to go for another short drive within the hour or so. Going to see if it happens again and if it does I'm going to lift it up and take a look underneath

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[PSUGOLD]

I had a noise like that last year, sounded like metallic vibration under the car in the back. I took it to my local guy who got it up, we found the heat shield had come loose and was vibrating. He put in a couple new fasteners and it was good to go. Maybe not the same thing, but worth taking a look at.

[cjw]

I had this a couple times. I stopped in a drive-through, then when I inched ahead, it sounded like I ran over a garbage can.

Checked underneath, nothing. Did a hard stop forward and backwards and it went away. Came back once, same thing. I'm assuming it was just a rock that was stuck.

EDIT: Also wiggled the brake shields and nothing was loose.

[lochs]

I had a noise like that last year, sounded like metallic vibration under the car in the back. I took it to my local guy who got it up, we found the heat shield had come loose and was vibrating. He put in a couple new fasteners and it was good to go. Maybe not the same thing, but worth taking a look at.

Was it a constant vibration or did it go away and come back?

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[lochs]

I had this a couple times. I stopped in a drive-through, then when I inched ahead, it sounded like I ran over a garbage can.

Checked underneath, nothing. Did a hard stop forward and backwards and it went away. Came back once, same thing. I'm assuming it was just a rock that was stuck.

At this moment I think it may have been a rock, because the noise has gone away, we'll see over the next few days if it returns or not

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[grovlet]

When you get a chance, try to get the car up and look around the wheels. Oddly enough, I had a wire coat hanger stuck in the undercarriage by the front passenger wheel and it would hit my wheel when I turned left. Didn't see it from underneath at first glance and kept getting this thud noise when turning left.

Be careful with stuff like this - I had a coat hanger get stuck like that in my GTI - turns out it was rubbing on the tire sidewall - and eventually it wore through the tire = Blowout: Luckily I was only cornering at around 35 MPH and it was on 40 series tires so they held enough to only make the car squirrelly but not 100% erratic - although I did need a new tire.....

[PSUGOLD]

Was it a constant vibration or did it go away and come back?

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It would come and go. It would be worst when i decelerated into a turn or when I slowly pulled off. Sounded horrible though, like something metal was going to fall off, but it was an easy fix once we found it.

[SteveYem]

Interesting, do you have any ideas about what would be wrong with the fuel pump? I'm going to go for another short drive within the hour or so. Going to see if it happens again and if it does I'm going to lift it up and take a look underneath

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No clue. I'm not even sure what noise a fuel pump would make (if any) when failing. Within the next few days I'm going to get the rear of the car up and take a look back there fore any loose heat shields or interference between heat shield and exhaust pipes, but I can't think of anything that's changed to cause an interference out of the blue.

[vwblackb5]

At this moment I think it may have been a rock, because the noise has gone away, we'll see over the next few days if it returns or not

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OP, it's most likely a pebble/rock that got wedged in the rotor dust shield. I had the same issue on my 2016 S4 with less than 1k miles a few months back. It made the most god awful scratching tin can noise, like you were dragging your exhaust on the ground. Jacked it up and saw a small pebble wedged in the rear dust shield from when I drove over a recently paved road. It's been 4k miles since then and it has not returned.

TL;DR .. most likely a pebble/rock wedged in rotor dust shield