....You know. I can't say I've even noticed a compartment down there! I'll look for it next time I'm out and about. It might be a fuse panel. Most newer vehicles have a smaller fuse panel under the dash and then larger fuses and relays are located under the hood. The only problem I had with my G6 was a loose screw in the front right speaker under the dash. Took the dealer 4 days on and off to diagnose and repair the problem. Service was terrible, perhaps we can help you pinpoint the rattle!
'11 Ram SXT 4x4 quad cab - 5.7L V8; 128,200kms
'09 Malibu 2Lt 3.6L - 140,000kms purchased 1 March 2019
'06 Pontiac G6 GT - 3.5L V6; 162,000kms (rear ended 15 Feb 2019, and given totalled title by insurance)