Thanks for the suggestions. Just wanted you to know that the cause has been found! Surprisingly enough, our mechanic had finally found the problem when we received the following e-mail from another source:
This may sound right off the wall here but have them pull the starter motor and check whether the starter drive return spring has not broken. This return spring is designed to hold the starter drive gear away from the engine s flywheel s ring gear after the engine has been started. When the spring breaks the starter drive can float on the starter armature and bounce off the rotating flywheel making a sound as you described.
The first one that I found drove me crazy looking for it because we could not reproduce it here in the shop. Like you said it would only do it making turns and no there never was any indication of a starter problem. Why only on turns is because the engine is transverse (sitting side ways) and the g-force of the turn forces the drive to slide out.
The second one was on a 99 Jimmy. Again with this spring broken the starter dive was allowed to slide back and hit the spinning flywheel. Jimmy s are rear or four wheel drive and the engine sits forwards between the wheels.
It'll only take them 10 or 15 minutes to pull the starter back and check this. So if I'm wrong you're not into a big expence.
AGAIN, THANKS FOR THE SUGGESTIONS -- THESE FORUMS ALWAYS AMAZE ME HOW SOMEONE COMES UP WITH THE RIGHT ANSWER.
Thursday, January 18th, 2007 AT 3:26 PM