busting 4049s

[km-r]

i built the DoubleD project from ROG but im experiencing some issues regarding the 4049,
the effect sounded well but after some time of playing it, the sound gets gated... could the chip been fried?
i tried replacing a new 4049, but same results, after 3mins the soud gates...
i placed a 150ohm resistor in series with the supply pin of the 4049, no improvement...

tried 4 chips in all...

[Paul Perry (Frostwave)]

When something using a CMOS chip consistently goes 'bad' over a number of minutes, it is usually a bias problem (a high value resistor slowly charging a cap and moving a circuit input out of working range) or else (less likely) the chip overheating & going out of operating conditions.
When a CMOS chip goes bad 'randomly' it's an input pin left unattached & moving up & down aimlessly.