Once you have cut a master laquer, you have metal stampers created and have records pressed from them. Discuss manufacturing here. (Record Matrix Electroforming- Plating, Vinyl Record Pressing.)
We always called it a dimple. Our American friends might call it a divot.
They will sound like a low frequency thump, as per your comparison to a kick drum
The question is... why are you getting them? How do you clean the mould and the back of the stamper?