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Hi Im Scott
The Charge rate of the Alternator must be checked if the alternator isnt charging correctly this can cause battery drain and then failure, if the mechanic replaced the battery without doing this then the new battery will eventually die.
The Mechanic replaced your battery. The Alternator's duty is to charge the battery. If your son's car is running rough due to power drain then the alternator is not keeping up the charge to the battery, you mention that after 1 week the car has become inoperable it may take this long in some cases for the battery to become drained enough to show similar symptoms as before if the alternator is not charging or is only partially charging.
Without hearing the womp sound you describe i can only assume that it is as a result of the vehicle misfiring as systems begin to shut down due to lack of voltage (battery flat).
If the noise you are describing occurs while the car is sitting still and not whilst moving there is no chance that it could be caused by a CV joint or Wheel bearing. If however it does occur whilst moving then yes it is entirely possible that it is a bearing or CV issue, but I can only assume your Mechanic would know this because it would be very obvious. As far as your problem with politely telling the Mechanic he is full of crap I would take the car elsewhere for a 2nd opinion and a little peace of mind.
Please dont hesitate to contact me if I can be of any further help ... thats why we are here after all.