Shant

I was driving my 2007 C4S tiptronic this morning. After about 2 minutes into the drive, at about 35 mph, I suddenly heard a very loud sound (from my car) that sounded like "metal scraping metal". Like the sound of a dozen forks screeching against a chalkboard.

After about 10 seconds into the sound, I slowed down to about 10 mph. The sound lessened as I decreased my speed (still pretty loud though). Then, after about 25 seconds from the time the sound began (and still rolling at 10 mph), the sound disappeared immediately.

After the sound disappeared, I found a place to pull my car over. I inspected the car and looked underneath. Nothing out of the ordinary. This entire day, and some 50 miles of driving since this morning, I have not heard any unusual noises from the car. I cannot duplicate anything. The car is driving fine.

I am truly at a loss as to what happened. I could not tell exactly where on the car the sound was coming from. For a second, I thought maybe my tailpipes were dragging on the street (THATS how loud the sound was). My best guess is that a foreign object (i.e. rock) got stuck somewhere in the wheelbase. Still cant be sure though.

Thoughts? This one puzzles me.

Mike in CA

Hard to say not having heard the sound, but a small stone getting wedged between the rotor and the backing plate/splash shield can make a pretty hellacious screech. This would also explain why the noise decreased as you slowed down. Usually the stone will get spit out and the noise will stop. Just a thought.

aaks38

Usually screechy sounds emanate from pulleys, and belt drive systems. Its possible you may have a bad pulley or bearing on its way out..Just check your serpentine belt and all of the pulleys it tracks.

Spiffyjiff

yep.

beyond that i've heard of a squealing clutch (or flywheel to be more exact) but i dont know what causes it, at what speeds, engaged/disengaged, etc.

Mike in CA

Possible, but it seems unlikely that the squeal/screech from a bad pully or belt would just start while driving along (not at start-up) then disappear completely after 25 seconds and not reccur, as described by the OP. A stone wedged temporarily behind the brake rotor would behave just as he described; my bet is still on that.

Maughan67

I had exactly the symptoms described by the OP a couple of times on a BMW 5 series I had a few years ago. It was caused by the stone explanation above.

Horrible noise. Very very loud. Sounded like the car was murdering itself. But all fine once the stone worked its way loose.

Matt

Dzu

Same car (not 4S), same sound. Maybe sound isn’t the same but video/phone mic might change the sound.
Same conditions, small bumps or small street holes, only on slow speed.
I tried to balance the car but i have PASM and is very hard. You need two strong guys to balance the car from the rear wheel arches and you sit inside.
It sounds like its from the rear axle from outside, but the noise its “traveling” and sitting inside the car i hear it in front.
check this, maybe you can hear it.
My opinion is that the exhaust might hit something, or a shock absorber..

GoldenGorilla

Usually its the throwout bearing. But that only happens when the clutch is pedal is pressed, which is not what the OP described.

PV997

This has happened to me twice on my DD Saab and it sounded exactly like the OP described. One time it spit out and the other I had to remove the wheel and fish it out. Definitely an incredibly loud (and embarrassing) screech as the thin metal of the backing plate vibrates and amplifies the sound. First time it happened right as I was picking up the kids at school, they tried to pretend they didn't know me.