It is completely normal and extremely common for snakes to have a inconstant and mild whistle as well as a slightly distended throat while in the middle of, or coming very close to, a shed cycle. That distention, whether it happens due to partial blockage of the airways caused by RI or while in shed or due to stuck shed on or in the nose, is due to having to breathe through the mouth rather than the nose. The whistling happens simply because the old skin is loosening and partially occluding(blocking) the airway through the nostrils. This clears up once the shed is complete, provided none of the old skin was retained for whatever reason in the nasal area. Sometimes the whistling and throat distention can occur due to substrate being in there as well.
RI noises sound VERY different from this and are much more constant, gurgle/raspy/gasping like in sound and nature, and usually quite pronounced. I know what you two were thinking.