What Causes the Engine Valves to Sometimes Make Noise and Sometimes Not?

[McRuby]

Car engine sometimes makes noise reasons are as follows: Valve leakage noise: Valve leakage noise occurs outside the valve chamber, mainly due to improper operation during valve seat reaming or excessive wear of the valve guide inner hole, causing the valve seat to tilt or the valve clearance to be too small, resulting in valve burning and incomplete valve closure leading to leakage noise. Valve tapping noise: During engine idle operation, a continuous tapping sound occurs between the valve stem tail and its driving component, which intensifies with increasing speed. The noise does not change with engine temperature variation or ignition interruption. Valve seat noise: The valve seat ring surface is rough, processing precision is unqualified, improper selection of seat ring interference causes looseness, improper material selection leads to excessive deformation after heating, or the valve seat fitting process does not meet requirements.