Chevrolet Repair: 1997 Lumina, 1000 marbles under hood turning left..., sheet metal screws, chevy lumina

Question
1997 4 Dr. Chevy Lumina Sedan, 136K miles, with AC, Anti-Lock Brakes (ALB), Power windows, locks, new power steering pump + belt, replaced ALB sensor passengrer side 2 yrs ago, excellent condition, commuter car (100 miles per day), oil changed every 4K miles, tires rotated,  brakes replaced, garaged, 90% highway driving,

Symptoms: Turning left, accelerating from stop or rounding turn (left) under acceleration, sound likes 1000 marbles rattling around under the hood.  Highly metalic.  Sound diminishes as the tranny shifts up...
> Same in warm or cold temps, can feel slightly under foot through gas pedal
> Use 87 octane gas and engine performs great, no valve detonation
> Straight-on acceleration minimal noise
> Turning right, minimal noise
> Took to my mechanic, he said it was catalytic converter shield and said he bent it to stop noise.  As I drove away the noise was still the same, BS artist..
> Put car on ramps, I got under the car with rubber mallet, pinged several area's (catalytic converter shield and nothing, exhaust pipe/manifold, nothing, drive axels, nothing, catalytic converter, nothing,
> Only noticable area was under hood, exhaust manifold shield,  above oil filter, used handle from rubber mallet and could get some noise similar but not really sure.  Clearances are very tight-shield to actual manifold, but just not sure that is it.  I put a couple of sheet metal screws between the shield and manifold to separate them to see if there was any change and no change occured...HELP...getting louder, I don't want to wreck my iron horse Lumina...  

Answer
Hi Mike, The sheilds don't know if your going straight or turning so this probably isn't your noise. The part that does know is your drive axle CV joint. This will make noise mostly on turns while your on the gas. I would try to locate the side it is on( have someone ride with you and take turns driving) then replace the axle shaft. You can buy a reman shaft for around 75 dollars which comes with new CV boots.

Let me know how you make out

Have a Nice Day     Mark