  We observe a strong negative magnetoresistance at non-quantizing magnetic
fields in a high-mobility two-dimensional electron gas (2DEG). This strong
negative magnetoresistance consists of a narrow peak around zero magnetic field
and a huge magnetoresistance at larger fields. The peak shows parabolic
magnetic field dependence and is attributed to the interplay of smooth disorder
and rare strong scatterers. We identify the rare strong scatterers as
macroscopic defects in the material and determine their density from the peak
curvature.
