Edward Loper, it sounds like you have a small leak in vent system. I think that you should do a peppermint oil test first to confirm that the odors are coming from the plumbing vent system. If the peppermint oil test confirms the source of the odors is from a vent leak, then the next step is to do a smoke test to locate the leak.
I recommend that you contract with a Licensed Master Plumber who is qualified to do the smoke test. Improper smoke test procedures can result in significant damage to the plumbing system in your home, or damage to the interior of your home. When you finally do locate the leak, repair it, and then do the peppermint oil test again to verify that you have been successful in eliminating the source of the odors in your kitchen. There may be more than one leak. JWA