these trucks will not shift into 4lo unless the truck is at a full stop with the clutch and brake pedals pressed with the electronic transfer case. so he obviously did that right. as for the noise, mine has always been loud in 4lo. i have beat the ever living **** out of my truck in 4hi and 4lo for the last 3 years with no transfer case issues. if your that worried about it take the balancer off the back of the case, only 4 bolts, and remove the fill plug. check the oil level and color. that will give you a pretty good idea of how the case is doing inside, unless the oil has recently been changed.
for what it is worth, every ranger i have wheeled with always whines in 4lo. same with every jeep and most fullsizes
2005 DSG ranger 4x4, 4.0L 5spd.
Dual magnaflow exhaust, 6000k HIDs, kenwood deck with 2 10" alpine subs
33x12.5 wrangler mt/r kevlars on 15x8 ultra nomads, shackles and cranked t-bars!!