failing torque converter clutch. needs replacement and do it asap otherwise the material flying round in there can take out the rest of the transmission.
the GM Chinese chrome wheels are awful. they don't last in the salt even if you take care of them. I got rid of my badly pitted chrome 20s for some AT4 wheels. They were so bad they wouldn't hold air. Where the bead seats it was just destroyed.
i had the tcc go out on mine and i guess i was lucky because they were able to flush the trans and there was no damage to it. just a new TCC and good to go.