Looks like a big ball of mud/dirt - indicating that it's most likely the nest of a mud dauber wasp. Nothing to be concerned about. Mud daubers are solitary wasps that do not guard/defend their nests. They just build those little mud cells, stock them with paralyzed prey (such as spiders or caterpillars, depenidng on the species of mud dauber), lay a single egg in the cell, then seal it up and move on to the next one.

Because it is in a very inconvenient spot - and you don't want chunks of it breaking off and dropping into your engine - I'd recommend breaking it up manually and removing it. Just be prepared for a bunch of seemingly-dead (but actually paralyzed) to fall out of it like some kind of creepy pinata.