I've had this issue for about 18 months now. Had a leaking vacuum pump, replaced it just before it got cold and it seemed like the noise went away with it. However, as soon as the warm weather returned, the noise returned.
This is my original thread below. I've dealt with a host of CCV leaks before and usually it's a whistling sound when a pipe cracks but I took it to an indy regardless and they did a smoke test and a compression test and everything checked out. Truck runs fine with no issues.
I was leaning towards pulleys/belts again but someone on here said they replaced theirs to no avail. Let's see if we can sort this out collectively...
https://www.xbimmers.com/forums/show....php?t=1467112