Audio problem: When Dean puts the cassette in the car stereo he reads 'Metallica' off it, yet AC/DC plays. [In the original version Metallica was played, but AC/DC was used in newer versions due to copyright issues.]
Audio problem: The pilot asks Amanda how she is at the start. When Amanda replies the audio doesn't match her mouth. (00:02:10)
Provenance - S1-E19
Audio problem: When Sarah goes to touch Evelyn's shoulder, you hear Sam's voice telling her to stop, except his mouth isn't moving at the time the phrase is being uttered. (00:23:50)
Answer: Angel blades come from angels. It's their angelic magic that makes it special. Therefore, an archangel blade is made magical with the powers of an archangel. They couldn't have just created one or used one, as none of them are archangels.