We experienced unusual acoustic vibration in the operation of in-line array tubular heat exchangers named gas heater. This vibration mode was not one dimensional in the direction perpendicular to gas flow and could not be vanished by inserting baffle plates into the tube bundle along the gas flow. So we had to confirm acoustic vibration characteristics using 3-dimensional air flow scale model. Here, we report this test results about multi-stage gas heater and some countermeasure methods. Especially we discovered that unusual acoustic vibration mentioned above did not appeared in the case of some staggerd tube array having same heat transfer characteristics as in-line tube array.