Thump-Thump-Thump ?? Panaracer Gravel King tires

I put these tires on my all-around bike - 650bx38. I like the tires over all - plenty of cushion and I have no problem keeping up with the other riders - no flats so far.

However. when riding on smooth pavement I notice a rhythmic thumping that corresponds to the portion of the tire that has the...