2001 impala "chatter" on acceleration

I recently had my daughter’s 2001 impala radiator replaced. Before the service, there were no other problems. After the service, immediately, upon acceleration, there was chatter, or wobble, that was not felt in the steering wheel. It sort of feels like a tire is out of balance, but only occurs upon acceleration, worse at around 1800 - 2000 rpm, 40-60 mph. When I back off on the gas, it goes away. The mechanic seems to think it is an axle. How did an axle get bent while replacing a radiator? (I know) What might have been removed/loosened while replacing the radiator that would cause this chatter, almost as though the parking brake is left on, partially? Motor mount? Motor brace?

It is setting at the mechanic’s now, awaiting time for him to get to it.