Loud abrasive pop underneath left rear

[LanderCT7]

Driving on highway and loud bang/pop came from under left rear side of car. Didn't repeat and car drove fine after the bang and since. Previously diagnosed with transmission leak and slippage with possible damage to clutch but since specialist corrected transmission fluid level, car has been driving without incident, no leaks, great performance for 2 weeks over 400 miles of driving. Taking in for regular service in a week. Any thoughts?