we tried to amplify the signal before buffering it and the output just becomes noisy as hell with or without the PIC connected.
So it's not a PIC problem, it's more a problem with the output of your sensor.

Is there any way to set PORTA.0 as a low impedance input???
With external hardware.


It's still not really clear to me what you are trying to achieve.

What does the timing of the analog signal look like?