98 Neon highline, transmission problems

Hello,

I've got a 98 Neon Highline, 4 cyl DOHC with an auto trans at about 60K miles. Recently about a year ago the transmission started making a whining noise at about 50K miles, when we put it into reverse (it does this with the car both hot and cold). I changed the trans fluid and filter and the problem is still there. All other gears are fine. Can anybody tell me what might be causing this, and/or is this something to be concerned with???

Thanks a lot!
--
Chris