Two problems related to differential unit have been reported for the 2003 Toyota Matrix. The most recently reported issues are listed below.
Noticed and increasing grinding noise coming from the transmission. Had the transmission fluid changed also having the mechanic look for metal shaving with none found. Took to transmission specialist who confirmed the "differential" was going to fail soon and advised to not drive the car until repaired.
Toyota differential failed at 100k. According to the mechanic, the problems must have been existent for a significant amount of time.