What is causing this rubbing sound from transmission?

Hello, There are several bearings in your transmission that can make this noise, but all of them require the same fix: rebuild or replace the transmission. Now if this is a manual transmission, you could have a slipping clutch, but you would notice the engine RPM high, but the vehicle speed low. For an automatic transmission, don't operate it any longer until you have corrected the issue. There could be an issue with the front pump. torque converter, or differential as well, but, again, you'll still need to pull the transmission, inspect, and replace damaged components. We may have a certified transmission shop in your area, just take a look at this link and see what is around: http://repairpal.com/chevrolet-within-10-miles-of-pasadena-texas-77504