95 buick lesabre tramission question

Hi, im new here and i hope someone can help me out. My daughter has a 95 buick lesabre with automatic transmission. She went to back out of the driveway today and reverse went out and it started making a loud knocking/rattleing noise. She drove it back up the driveway and got me to look at it. When i put it in park or neutral and it's idleing ,it still makes the noise, but when i put it in any of the drive positions, the noise goes away. And then when i throw it in reverse, neutral, or park the noise comes back. It almost sounds like a engine knock, but i would think an engine knock would be constant. Any help would be appreciated.....thanks,john :banghead:

If you lost reverse, then the tranny is the problem. It probably needs to be rebuilt, depending on how many miles are on it.