hi bud,ithink the sound you are hearing is coming from your gear box,its hard to say over the internet but most td5 g/boxes start to suffer from a noise on start up,its not to serious as far as i understand its a bush on the input shaft that is lubricated by splash,when they get a bit older the bush turns in the casing until it expands with heat witch gives that sound,i work at td5s that have done this for years,so providing this is what you are hearing you dont need to panic.