I watched ahead a bit more in Japanese to investigate, and thankfully, nothing else was ruined, including the closing credits. Just to confirm, I also have Seasons 3 and 4, and the Japanese opening titles have never sounded this way.
Although that does bring up another issue. My Season 4 set had a problem with the opening too. The sound is fine, but the audio and video will skip for like a split second every second or two in certain parts. At first I thought the DVD was damaged, but then I decided that couldn't be the case when all six discs exhibited the same errors, and in seemingly the same spots. Continuing past the opening title, it would seem that the rest of the Japanese track has the same tiny glitches. Switch to English audio though and the problem vanishes. Also weird is that the Japanese closing titles are fine.
My question is has anyone else encountered these glitches / poor audio? Also, regarding Season 5, why wouldn't Funi simply take the same opening title from the previous set and use that? Does anybody ever watch these before they make a million copies and ship them?

P.S. Apologies if this is the wrong forum or if a thread already exists for this. Didn't see anything for Season 5, and as for Season 4, didn't want to necro-post.