The usual causes for a thumping sound are a split drum weld or bad drum rollers, or both. You already identified the drum weld issue, which is quite common these days with the super-thin metal they use to make drums. You can darn near see thru them if they were any flimsier.
There is an LG dryer manual in the front of this forum, so look into it and see if you want to take the dryer apart to replace the drum or not. (Since we don't know your mechanical abilities, it would be silly of us to say if a job was "easy" or not. To us, everything is easy because we do it all day long.) Use your model number to look up the drum from the boxes on the left side of this page if you are curious as to the prices, etc of the parts.