You didn't give any info on what car you have, how many miles, etc., but I have one possibility. The early CRX Si's (possibly others as well) threw transmission main bearings around 180,000 to 220,000 miles. The way you could tell was noise in the transmission, and clutch slippage as the bearing seal gets torn up and oil gets on the clutch. I don't know about the axles popping.