More About Points »
It could be brake related. Try driving down an alley with buildings/walls on both sides, roll the windows down and drive slowly - See if you can determine which side the sound is coming from. If the sound is more pronounced on one side or the other, it may be brake or suspension related. If the sound seems to be central, it may be axle/differential related.
It may be a security related issue. How many miles can you travel before the vehicle shuts itself down? If the vehicle shuts down before you can make any progress it is likely a security related issue. If a few miles can be driven before shutdown it is likely something else. Did you do the work yourself or at a repair facility? If performed by a facility, it should be under warranty.
If the A/C refrigerant was recently recharged and now the cooling capability is diminished, there is likely a leak. Was dye added when the recharge was performed? More importantly, was the system pressure tested to EPA standards to ensure it holds a vacuum? The vacuum test ensures there are no leaks otherwise ambient air is sucked into the system and the pressure test fails.
While troubleshooting from a chair miles away can be problematic, if I had to guess and given what was mentioned regarding the task of putting the vehicle into park, drive, park I might take a look at the shift interlock solenoid. If a failing/failed shift interlock solenoid is telling the car it is still in drive, it would prohibit release of the key.