Ok, I have this sound coming from the front of the vehicle (grinding or scraping) that occurs when I accelerate beyond a certain point. Then when the gear changes, it goes away; actually, it may or may not occur with gear changes. However, it does seem that way... Of note, the sound only lasts a brief second, then disappears until the next "aggressive" depression of the accelerator.

Here's my question: In my research, I've come up with possible causes. These are: 1) heat shield issue. The mechanic did seem to warp the heat shield when he needed to gain access from the front end to remove an old O2 sensor; 2) engine or transmission mount; 3) stuck caliper; 4) pre-cat O2 sensor aluminum shield (not sure we have one of these); 5) exhaust mount; 6) front wheel bearing; 7) something with the air intake system; 8) something going on with the transmission.

Hoping it's #8, as still have warranty on that from tranny replacement ~ 1 yr. ago. or #1, as the mechanic will have to remedy that for $0 as he caused the damage.

Any input on the likely cause, IYO, is appreciated...

 

As you've mentioned, there are just so many possibilities. Try to really pinpoint what action causes the sound. Does it occur at a certain RPM? Does it happen when going through the entire RPM range in neutral? Or only when it's in gear?

If its an automatic, try using the sport drive mode instead the regular mode. Any change? Also, try to find if it's speed related.

I've had a few noises from the front end that have been minor and quick fixes. One was the thin shielding around the rotor was gently rubbing on the rotor at certain times after some front end work. Just had to take the wheel off and bend it back in place. Another was improperly engineered stabilizer bar links that were rubbing on the CV axle under a certain braking pressure.

 

Take note of the engine RPM when this occurs. My money is on the heat shield, loose baffle in silencer or some other thin metal making a harmonic resonance from vibration - the kind of vibration that occurs at a specific RPM. The exhaust mount is plausible also.

 

Will be heading to MINI shop tomorrow. Will ask mechanic to go on a test drive with me. Will point out the problem and let him diagnose/fix. Doesn't strike me as serious, just annoying.