PC PSU monitor

Hey guys gals

I built a PC PSU monitor

It has LEDS and a piezo buzzer to indicate low or high volts on the 12v 5v 3v3 power rails on the PSU for PC

The problem is that it beeps when shutting down

The residual voltage (at the PSU) at shutdown causes the Piezo to sound off as it is going through a low voltage alarm cos there is some voltage decaying

Please see fotos of schematic

I have tried the diodes

I have tried reducing the cap 100uF tried 10uF no joy

I will also try using a cap at the Base of Q1 to ground

There is the option to use relays to cut the voltage off sharp so there would be no residual voltage

But that is way too complex, I will use 6 PSU monitors and that means 13 relays, a power up circuit and power down circuit

Way too complex a setup

Maybe a NPN tranny to sharply cut the supply voltage to the units, but I dont know the math to figure that out

But for now any suggestion please

How it works
LED1 & LED5 are at the top & bottom of the monitoring range
If they light up they draw current and subsequently Q1 turns ON
Q1 conducts current and the Piezo sounds off