It sounds like a power problem. I've had a similar problem only to figure out I was having power problems. If the drive isn't getting power constantly it can cause this.
Since you say the solutions mentioned in the other threads didn't fix the issue I'm going to assume you've tried them? New/different USB cable, different USB port, etc. Can you power the drive without using the inverter? Can you use an extension chord and plug it into a wall plug to try and eliminate the inverter as the cause?
Has it always done this or has it just started doing this?