2004 Impala 3.4L 4t65e whine in passing gear

Hello,
I had the transmission rebuilt about 5,000 miles ago. Grocery-getter never put it into passing gear until recently, and then I heard a whinning sound. Works great other than noise in passing gear. Fluid level ok, but a couple bubbles on dipstick. Sucking in air somewhere?
Thanks for input you may have.

There should be no air in the trans oil. A pump pickup (filter) leak could create foaming, or a dropped oil tube for the differential and accumulators could be leaking. It could also be a pump seal, or overfilled/underfilled trans.