Why can endocarditis cause a heart murmur?

Endocarditis is inflammation of the inner layer of the heart

Murmur is the sound of blowing fluid (air or liquid) in a manner which causes turbulence (just like blowing air into a whistle).

Endocarditis damages the valves of the heart (making them bigger or smaller in diameter). This will lead to turbulence of blood, and so murmur.

so the inner layer of the heart constitute the heart valves, and when the heart valves are inflammed the may become stenosed( narrowed) or dilated ( widened) and that effect on the structure of the valves affect the blood flow throw them and causes the musical sound ( the murmurs).

Endocarditis is the inflammation of the endocardium and this latter constitutes the cardiac valves.

When the endocardium is inflammed the surface becomes swollen thus disrupting the smooth lining of the endocardium and the valve leaflets .

The roughness of the surface causes TURBULENCE flow of the blood . It is this turbulence of the blood flow aver the roughened surfaces that is heard as a murmur through the stethoscope.

Hope this answers your question.