Having an issue with the RTC and really confused on how its behaving like this...

I have a piezo sensor being used as vibration knock sensor. On a Proto1 Shield using A1 pad. I have tested this alone with the core board + usb shield and everything works fine.

Moving on, core board + usb shield + rtc shield. flash it, set time, call time and works as expected.

Now, looking at the spec section here it seems that RTC uses A4 and A5. But when I put the 2 shields together and go back to testing the piezo, i'm getting a fixed voltage 1 second pulsed signal on A1. Very odd. If i knock on the piezo it disturbs the voltage. but still is pulsing.
So serial monitor looks like this (using AnalogRead simple code)

0
0
0
0
788
788
788
788
788
0
0
0
0
ect

Have already tried A0 as well as is doing the same thing. Looks like the two aren't playing nicely together and i cant figure out why. RTC is super simple and uses A4/A5 so should be separate from everything else correct?

Any help greatly appreciated!