Any recent repairs?
Does the starter make any noise at all?
Do the lights dim when the key is turned to start?
Any aftermarket devices installed (alarm, keyless, etc..)?
It makes the noise when the ignition is turned to RUN or to START?
Does it sound like the noise is coming from the starter?
Ok, which V8 do you have so I can look at the schematics?
5.3L with 8th vin digit B
5.3L with 8th vin digit T
5.3L with 8th vin digit Z