When I first start it it makes a pinging or tapping noise, I think we used to

The oil is too thick and needs changed.If it only does it when it's cold.

Could be oil related. May have valve lifter that takes a while to pump up. But most likely it is an exhaust leak at the manifold. They can make a fairly heavy tapping/pinging noise cold. The manifold warms up & expands, thus the noise goes away.