[s-cars] got a new sound

[Tom Green]

Since you don't feel anything, I would suspect it is not driveline  
related.
Any small driveline vibration is usually easily felt in the seat of  
the pants.
I would look carefully at the heat shields  for a loose piece that  
vibrates
in the airflow.

Tom

> Date: Sun, 16 Mar 2008 13:33:56 -0400
> From: Mike Fitton <rfitton at vt.edu>
> Subject: [s-cars] got a new sound
> To: s-car-list <s-car-list at audifans.com>
> Message-ID: <47DD5A04.7070002 at vt.edu>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> And I'm at a total loss.  It's a very clean vibration.  Don't feel it,
> only hear it.  Frequency rises with ground speed.  Amplitude  
> varies.  I
> don't hear it below about 20mph and not above about 65mph.  It's  
> loudest
> around 50-55mph.
>
> I've ruled out everything engine by turning the engine off at 55mph in
> neutral.  Stick and clutch position don't change anything.  Steering
> wheel doesn't change anything.  Wheel bearings all pass the
> autocrosser's tech inspection test.  All CV boots are tear-free as far
> as I can tell, and none of the usual grease sling that comes with torn
> boots.  No perceptible alignment changes.  No corollary bugs at all  
> that
> I've noticed.
>
> About two months ago, I changed out my transmission oil (finally).
> Amsoil's synthetic 75W90 GL4.  All the plugs are still tight and the
> stick still feels great.  The sound started very suddenly about a week
> ago, so I'm guessing it's not that.
>
> Two weeks ago (one week before the sound started) I switched back  
> to my
> summer tires.  Drove on those just fine for the first week.  Pressures
> are consistent.  Verified lug torque at 90 lb-ft for all 20.  Rotated
> them anyway with no change.  Tires and wheels all look fine, and no
> feeling of imbalance in the drivetrain.
>
> All I can think of is the prop shaft center bearing.  I've never
> experienced that before, so I don't know how it should sound.  I  
> played
> with my prop shaft (no Krausky, not like sexually; or at least not  
> right
> then) and found a little front to back play which seems like it  
> would be
> normal with a CV joint on either side.  The two halves seem to move
> equally during this exercise.  There's also a little play  
> perpendicular
> to the shaft at the center - that is, I can bend it up/down/left/ 
> right a
> little at the center U joint.  I never did that before, so I don't  
> know
> what's normal there.  But it seems to me like it shouldn't do that, so
> that's my best guess so far.
>
> But before I give up on diagnosis and resort to just throwing parts at
> it, I want some second opinions.  Anyone?  Bueller?
>
> -Cheers!
> Mike