New MJ Creditor -- Back of the Line, Buddy

Michael Jackson's estate is taking hits from all sides -- and big surprise, the newest creditor to enter the ring is a company that claims it's owed money for helping MJ refinance the MIJAC catalog.

According to a creditor's claim filed in L.A. Superior Court, MJ's estate owes $328,299.03 in unpaid fees to a small investment banking firm in Baltimore called Signal Hill Capital -- for "financial services related to music publishing assets."

As TMZ reported, the grand total for all creditors' claims against Jackson's estate is expected to exceed $20 million -- so a couple hundred grand here and there is pretty much small potatoes.