I sold a 210 and shipped it via UPS from WA to OK. The cab is a 600w 4 ohm cab that I never pushed beyond volume level 2 on my 500w amp. I never pushed it hard at all. It sounded perfectly normal before I shipped it. The buyer says it sounds crackly and distorted. I asked if the box was damaged and he said one corner looks pushed in but the cab didn't look damaged? What could be causing this issue? He's playing through a 450w head into the cab.