They are indeed shock waves aardvark2zz, not in the league of the big beggars we used to see in earlier days when we flew fast, but shock waves nonetheless.
The reason that we see them is because the vast majority of commercial jets are Trans-Sonic, not Sub-Sonic as suggested in the title of your thread. (There are some good folk oft appearing on these threads that still believe that we limit operating speeds to below Mcrit).
Regards,
Old Smokey