Been going on for some time - Savage used to snark at Levin, too. Dunno about recently.
It started with Savage attacking Hannity and Rush, etc. They never responded to it, but Levin did for them. I like Savage, but he has an inferiority complex and he should not. When he is on, he may be the best radio show in the country.
It might be that savage is always taking potshots at everyone else.