Cracking in the drive train

Hey guys, with my Legacy bj ’05; 3.0R; 6 gear switch I have a cracking / tension in the drivetrain. The problem only occurs in the warm condition, if you steer in during a slow drive, e.g. parking. After a ride of 50 km it comes only with almost full impact and if you drive longer (200km) it occurs already, if you hit the steering wheel only by 90°. You notice correctly like something blocked, which then dissolves with a cracking again. I have already stumbled through the forums and stumbled over the visco coupling/wheel coupling. Can they cause this problem? And the usual stupid questions: How expensive is the fun? Are there cheaper spare parts in the accessories? Can I do this myself? Thanks already for your help, mfG Birdy