Heat shield, or underbody panel or stiffener panel loose. Get car in the air safely and then...

I've noticed a new sound which seem to be getting a little worse. It is most prevalent on cold (22F) mornings.
It sounds like driver's side, underneath, aft of the door. For lack of a better description, I would say it sounds like a playing card held against a flywheel (but it isn't the flywheel) within the first 5-10 feet leaving the driveway, I hear it for about 2 seconds, and then I hear it when cornering under moderate power. It goes away when the car warms up.

I looked at all the panels in the wheel wells, and they are all secure.

The sound is not related to steering/turning. It is definitely drivetrain-related.
When I blip the throttle with the clutch in, no sound, therefore I can rule out water pump, AC compressor, etc.
Similarly, transmission in neutral, clutch engaged, no sound. When in gear, and I accelerate, even mildly, I get it pretty consistently. Only during acceleration, not at a steady speed.
Also, once the car warms to 180, no more sound.
Any ideas?

Some resonances might occur only with the engine under load.

Minus 40 degrees... Is that Fahrenheit or Celsius?

from under the car check all panels/shields/etc for any looseness. My Boxster lost a couple of nuts off the stiffener panel that until I replaced them had a bit of an intermittent rattle/buzz like a loose shield.

Once I had a loose wheel well liner that only made contact with the ground at speed and when it did created a very hard to diagnose/isolate noise. I noticed the liner's leading edge seriously abraded which gave me the clue.

But you have to get under the car.

Sincerely,

MarcW.

I'll check that. That was my first thought also, but didn't see anything obvious.

every panel with your fist and just see if you can find something loose, something that makes much if any noise when you hit it.


Go around the underside of the car several times until you get a feel. In doing so you'll develop a sense of what's normal noise when you hit something, or what's normal movement when you grab and shake something so when you encounter the loose item (if it exists) you'll know it.

Sincerely,

MarcW.

dghii
2000 Boxster S 6speed 112k miles

I have the original motor mount. I looked at it yesterday, had my son rev the engine while I looked for movement. Didn't see any, but that doesn't mean much. I'll put it on the lift this weekend.

dghii
2000 Boxster S 6speed 112k miles

Does any of this sound like a clutch issue? The reason I ask is that I have noticed what may some clutch sliippage during hard acceleration. If so, is there any troubleshooting I should try short of dropping the transmission to check?

Actually, I am itching to do that anyway, but I was hoping for warm weather first.

That sounds very much like a motor mount noise. Another possible culprit is clutch throwout bearing, but that tends more to be a "squeal" and will make the noise whenever the clutch isn't in.

When you talk about clutch slippage, what do you mean? Clutch slippage in these cars is very, very rare since the clutches are pretty strong. If you feel a sudden loss of power under hard acceleration it is probably not clutch slippage - either your MAF is going or your O2 sensors are going.

1998 986 Turbo-Look Cab
172,000 Miles
Dilithium Crystal Supercharger

I feel what I think is clutch slippage when I am accelerating through the gears. As I shift into a higher gear (most noticeable in 3rd and 4th) and release the clutch, there is about a second when it feels like the clutch pedal is still pressed slightly. I only notice it when accelerating hard.

I will put it on a lift this weekend and let you know what I find. Are there any telltale signs for a failing motor mount? I know about the hard shifting and the motor moving when revved. anything else?

OK, a few thoughts.

What you are describing as clutch slippage sounds more like clutch sticking - this is what happens when your clutch master cylinder isn't working right. How old is you brake fluid? Clutch master and slave run off the same system as the brakes, if your brake fluid is old you probably have bubbles in the system which is why your clutch master cylinder isn't engaging/disengaging properly. The cylinder itself could be bad too, but that is unusual. Easy solution is to to a clutch bleed - if you get bubbles, you found your problem. The nipple is on the driver's side of the transmission - it is messy and a pain, but not difficult.

Your noise could be related to the need for a clutch cylinder bleed - it could explain why the noise goes away when the car warms up. But it could still be the motor mount. Only way to really Dx the motor mount is to look at it, either by removing it or using a scope. But a secondary way is to get a sense if the motor is shifting - I have found this out by very hard cornering under engine load - forces the mount to move around and you can feel/hear the vibration - it should be reminiscent of a wheel rubbing on the wheel well.

1998 986 Turbo-Look Cab
172,000 Miles
Dilithium Crystal Supercharger

for the record, my clutch held with the material torn into pieces on the race track once. They dont just start to slowly slip. It goes from holding to shuddering upon engagement to dead. IME anyway.

Grant