Automatic clunk when below freezing?

Ok so Im new to automatics. Always had manuals. Well this morning it was 19 out and i turned her on and threw her in reverse and heard a loud clunk. Then threw it in drive and another loud clunk. It stopped once It warmed up. Im guessing the trans was just cold and the fluid was not warmed up. Any thoughts on this? Its only happened once. Later today after it cooled off I tried to make it happen again and nothing.

searched and only came up with OME clunk. Maybe I'm wording my search wrong.

 

My first thought is a U-joint but that would likely be in any weather.

 

Read that but every other time has been dead silent. Only has 15k on the trans so I'm hopping its alright. Im hoping it was just because it was cold and i threw it in reverse to quick.