I have a 97 GMC with a 4L60E transmission behind a 350 engine. I noticed a couple days ago when the transmission shifts into 4th there is a buzz or moan when it does this, right before the converter locks. The fluid and filter was changed approx 2500 miles ago. I have a transmission cooler installed.
The trans was rebuilt about 74K due to fwd clutch drum failure. The current mileage is now 87K. After the rebuild I used a magnafine filter in the return line to catch any strays the shop may have missed. I recently removed it and there were no particles out of the ordinary or in the pan during fluid and filter change.
Thanks for any ideas you all may have.