I am using a Klein non contact voltage detector and when the power is switched on I get a fast steady beep. And when I switch the breaker off I get a slow beep. Does this mean I am safe to cut the wires?
Have you read the user guide included with the tester? What is the model number?
I think Klein testers have a fast beep for higher voltages (48-1000 volts), and a slow beep for lower voltages (12-48 volts).
I'd use a multimeter (volt meter) to test the wires for voltage. It could be that the non-contact tester is picking up phantom voltage, but you'll want to be sure before cutting the cable.
If you have internet over the power lines, you could be picking that up.
I have the Kline NCVT-1 and a slow beep at an AC outlet when putting the tip into either the Neutral or Ground means it is picking up phantom voltage in the range of 2.0 to 30 volts AC. It turned out that the circuit I was testing had an open Ground back to the service panel. I found out that I had an open ground using a Ideal circuit tester 61-051. But the Kline Voltage tester was the tool that showed there was an issue with the Circuit in the first place after replacing an outlet within the circuit. After fixing the ground wire issue; the Kline voltage tester would then show a red light fast beep in the hot slot. It showed green with no beep in the Neutral and Ground slot of all recpticals I tested on the particular circuit. Nice little tool for testing the presence of electricity.