Hamman's sign is seen in-
hamman sign is a feature of pnuemo mediastinum Hamman's sign (rarely, Hammond's sign or Hammond's crunch) is a crunching, rasping sound, synchronous with the heabeat, heard over the precordium in spontaneous mediastinal emphysema. It is felt to result from the hea beating against air-filled tissues. It is named after Johns Hopkins clinician Louis Hamman, M.D. Ref Davidson 23rd edition pg 440
Pneumomediastinum
Pericardial effusion
SVC obstruction
Thyrotoxicosis
C.V.S