My son has a 2002 Impala and has complained of the same noise for about a month. He finally drove it to my house (about 100 miles) for me to check out. I removed the belt and the noise was still present. Next I jacked up the car and listened underneath. A lot louder so we shut it off, put the car on stands and I pulled the inspection cover to have a look at the torque convertor bolts. I found that the flexplate was cracked in three places from the large holes up to the crank mount area. His had progressed from a ticking to a very loud ticking/rubbing sound, hard to describe but if your Impala has the same problem it will get worse. His is a 3.4L engine with about 80k miles. I didn't want to risk further damage if everything started flying apart so it was trailered to the tranny shop about an hour ago. It should be ready Monday and I'll only be $500 poorer. Merry Christmas son
Chellbug here is a photo of the flexplate from my sons 02. I could only see the ends of the 3 cracks around the big holes. As you can see the center is cracked all the way around. I really do not know why it held together. The tech that repaired the car said he has done a lot of these.
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