This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
Clicking noise in pneumomediastinum is known as 
Select and explain. 
A. Hamman sign, B. Trail sign, C. Kussmaul sign, D. none
A: Hamman sign
Answer: A: Hamman sign 
Explanation: In pneumomediastinum,physical examination reveals subcutaneous emphysema in the suprasternal notch and Hamman's sign,which is a crunching or clicking noise synchronous with the heabeat and is best heard in the left lateral decubitus position.Kussmaul's sign is defined by either a rise or a lack of fall of the JVP with inspiration and is classically associated with constrictive pericarditis,restrictive cardiomyopathy,massive pulmonary embolism,right ventricular infarction,and advanced left ventricular systolic hea failure.Trail sign is the prominence of Sternocleidomastoid muscle on the side of tracheal detion. Ref:Harrison's medicine-18th edition,page no:2182,1823