An avalanche photodetector (APD) based on the AlxIn1-xAsySb1-y digital alloy materials system has recently attracted extensive attention due to its extremely low excess noise. Device defects are a critical factor limiting the performance of APDs. In this work, we use low frequency noise spectroscopy (LFNS) to characterize the property of the defects in AlxIn1-xAsySb1-y APDs grown by molecular beam epitaxy (MBE) using the digital alloy technique. Based on low frequency noise spectroscopy results carried out before and after device oxidation, two surface defects and one bulk defect have been identified, which could provide useful information for the future optimization the material growth and device fabrication processes.