Consider yourself lucky! I had a small acorn get under the foam tray and in the drain below! Had to use a borescope to find it. Was able to remove it with one of those extended reach tools (link below) without tearing everything apart.
Easiest way to clear I found is to use a short length of something like plastic refrigerator water supply tubing. The drip tray drain hose end is right in the mud flap/ trim piece. It is white 3/8" plastic tbg. Simply insert the small tubing up from below and flush out with some water until clear. Easy.
http://www.mscdirect.com/product/details/06574966 it is not magnetic. It has 4 small hook teeth that open when depressing plunger.
PS Buy the drain covers. They save a lot of grief. https:
https://www.ecstuning.com/Search/SiteSearch/Drain_Cover/ES2065693/
PSS: Check your front drains, I think they actually collect leaves easier than the rear and are harder to inspect. I made a pair of stainless wire screens for my front drains. They work very well.