You say "DC Transformer", but what you really need is pure DC from a real DC supply. If you're using something like an HO transformer, some of them are pretty noisy electrically, and would likely be worse than AC. Second best is a pure sine wave AC transformer, they seem to work as well as my DC bench supply.
If you're getting errors and retries on writing the FLASH or sound files, I'd adjust the setup and load them again.
