Why does fibrosis of the left ventricular posterior wall ( like in cases of muscular dist. )cause a murmur? where is the murmur coming from?

Murmurs from valves: Murmurs are heard when listening to the heart, and are caused by turbulent blood flow through the heart valves. The timing, type and location of the murmur can be used to identify which valve is involved. To further define the problem, an echocardiogram is used to see the blood flow in real time. Fibrosis of the ventricular wall does not cause a murmur, unless it effects the valves.

Heart disease: Posterior wall fibrosis can cause papillary muscle dysfunction and mitral insufficiency and the murmur of mitral insufficiency.