'97 Lexus ES300 Noise When Reversing Issue

[mparmar]

Hello,

I was hoping to get an idea of what's wrong with my car.

Every once in a while, when I reverse my 1997 ES300 (147,000 Miles) in the morning, it makes a noise when I am reversing. It's kind of this vibrating/grinding noise when I'm going down the driveway. I went ahead and did an automatic transmission flush/fill and it did not correct the problem. It does not happen everyday, but maybe every three to four days. It won't happen when I drive for the rest of the day either. My driveway is pretty steep, but I have never had a problem before as I always use the parking brake.

I was wondering if anyone had insight into what the problem could be.
Any help would appreciated. Thanks.

Mike