Cheap mufflers get louder over time because they use substandard packing that burns out.
Megan actually makes decent parts at the right price point.

The reason they get quieter is the packing burns in, that is, all the free space between the packing gets filled with carbon and packs itself tighter, thus making everything quieter.

and as for a "chrome" weld, that makes no sense. Megan mufflers are polished stainless steel, nothing about them is chrome.

Post some pics of the welds in question