After great help from Rdl (Big props, Dude!) he narrowed it down to three Options:
- Provider could have incomplete corrupted files (unlikely)
- HDD errors
- RAM Errors
I've monitored the occurrances of CRC-Errors and found out, it is a combination of RAM and HDD, caused by myself: whenever I was watching Video from my incoming-folder, there was not enough buffer, which caused HDD conflicts.
So thank you again, Rdl!
Thank you, Dacain, for your epic PMs with the right settings!
Problem solved, thread can be closed!