Title says it all. Finally decided to buy a PS4 to play some exclusives I can't get on PC, and I had to turn off Bloodborne after 30 minutes because of the NON STOP disc reading. I pressed the option button and it looks like the game is fully installed (28-ish GB), so I don't think it's still installing while I'm playing. Even if it was, though, I'd think the disc would be consistently spinning at speed, not up/down/up/down.

It's a high pitched motor spinning sound, not a crunch, grind, buzz or vibration. It's the same sound you hear when the disc first starts spinning up, like a far away dentist drill, but it never stops. Spin up for a second, spin down. Spin up, spin down. Wee! Oooh. Wee! Oooh. Wee! Oooh.

Is this normal?

No, it's not normal. The disc shouldn't be spinning at all after you've booted up the game.

No, this didn't happen for me.

@fredchuckdave: EXACTLY! lol.

It's this, right here, just a bit more rhythmic and not so random. This exact sound.

https://m.youtube.com/watch?v=8wLIyLFIVSs

Sure it's not the Tardis?

Either way, return it or send it to Sony. When I had a PS3 issue last year, I found Sony's UK support line rather helpful (even when they said they wouldn't be able to fix the issue).

my ps3 has started to do the same with discs mostly because it has gotten old. its sounds like its constantly trying to read something of the dics even when its not needed. without knowing to much about it it really sounds like the disc drive is having some issues. so if its brand new try trading it in for a new one. that should help. also buy then digital will also reduce it.
basically what i think the problem is is that its either a problem with some joints in the disc reader or the actual reading of the disc.
but again im just guessing, i dont have extensive knowledge about this

Problem solved, and I'll leave the result here in case anyone in the future needs it.

After some googling, it appears Bloodborne acts very weird if you play it before it's FULLY installed. I initially started as soon as the patch was downloaded, but this time I deleted the game entirely, put the disc back in, and left it alone for about an hour. Once it was completely installed, it started back up fine with no crazy disc accessing.

Seems to be unique to Bloodborne because I didn't have the same issue with Batman. So there it is, person from the future who is reading this. That's how you fix it.