In some cases when you go from a 20W50 viscosity to a 15W viscosity, engine noise may be more audible. A 20W viscosity is a thicker oil and this gives a numbing effect.It is just like adding a bottle of SAE40 oil treatment.
On the question of tappet noise, if you follow the threads, there have been comments from some zth members with regards to motor oils that do not cause tappets to be noisy. We are impartial on the choice of motor oils to blend with Tufoil. We will always leave this decision to members.
The addition of Tufoil will free internal engine surfaces and bearings of friction. Moving parts now thrive in this low friction medium and they move effortlessly.You may or may not experience a more noisy engine initially. It is difficult to compare between engines for no two engines are alike.But there is no question of a petrol engine " roaring " like a diesel. In all these years, the feedback is that engines are more quiet with the use of Tufoil.And there are many out there who can say on this.
