Nissan Xtrail Abnormal Sound in Multiple

Hello friends again here, I still annoy with the behavior of the Nissan Xtrail 2003, when it is a good time working and getting to a place where I must lower the speed, example when parking, I leave a sound of TAC TAC TAC TACTATICTACTAC on the side of the tubes on the engine, which are aluminum color, I said it is the multiple, I do not know what is due to this sound? That I must do, the mechanics do not tell me anything and it really bothers me, also when I am on the road, the engine is heard a little strong. Another question, in the same low revolutions a short grinding is heard by the axes will be that something must be lubricated

Friend The theme of noise is a bit complicated because what you listen to as a tactac, I can hear it as pafpafpaf, now it can be a valve that sounds, it can be a small valve that is mounted on the cylinder cover that allows the air passing to the multiple that causes a noise that is normal, while it is not very strong. But if it is a dry noise, then it is motor valve, try if the noise persists, the admission multiple can only do a noise class that is air aspiration. luck