Grrr - Invisible LP Scratch

I bought Norah Jones' new release on vinyl from Acoustic Sounds. I have a few of her prior releases on vinyl and the sound quality convinced me to go vinyl once again. First couple of plays and no problems but last night I play side 2 and there is a pop all the way through an entire track. I take it off, inspect and see absolutely nothing, put it on my VPI RCM and it's still there just the same. Even under a 10x magnifier I can see nothing, but it's a loud pop every time the record goes round for about 3 minutes. I have no clue what's causing this...anyone?

 

I have this very same problem on one of my used lps, but it's more as if the stylus hits something (loud CRACK ! at some point of a song) . Visually I detect nothing; learned to live with it.

 

It started after some play throughs were OK? odd

 

Seems as if your stylus or something/somebody else inflicted some non-visible damage to the groove, or a defect in the material was waiting to rear its ugly head.