-G-

I was on off road trip with my 270cdi G wagon yesterday , few times I changed tc low/high everything was ok, low and high mode worked properly. But after I came to normal road and in high mode I hear noise but I dont know from which part of car, its like gearbox because when in lower rpm you can hear little noise, but in higher 3000 or 4000 its more loud.And when gearbox in P its the same you can hear it with higher rpm. I checked system and everything without errors. Im afraid whats bad. gearbox fluid level is ok. Any suggestions? Sorry for my english...