[muddog321]

I'd look at a few of the common stranger things that I have had.
1. PCV valve rattle mormost at idle comes along the throttle cable if the plastic tie down on the drivers side of the intake breaks off - common after lower intake done. Resecure and possible PCV valve replace if aftermarket and check the valve cover grommet - yep it happens.
2. 99-01 have secondary air injection and that has check valves in the exhaust manifolds that always fail - internal spring and also rust out - see info in the How To on these.
3. Now if a more gurgaling sound thats the heater core.
4. Then possible relay chatter so listen in the underhood block or behind the glove box is the flasher/blinker one.
Hope its one of them!