Good day guys!

Help me I'm confused on what's going on with my car. By the way this is a project car. I have a lancer cb 1996 with Evolution 4 on it including AWD, AYC, ABS. I'm confused because some of my friends say that I should only change the transfer case oils and the whining and grinding will be off. But some of my friends says that I should replace my transfer case. When I drive my car 10-20kph the grinding and whining sound appears. But when I tried lifting the car and drive it the whining sound went off. So now I'm confused. Help me decipher the problem on my project car. I uploaded the videos on youtube and here's the link of what I'm saying.

Whining/grinding sound: Whining/grinding sound disappeared: Video on the transfer case when I lifted the car:
hope you could help me guys! Thanks!