Hmmm, from your description i was thinking the car is detonating under a load. Does it sound like engine noise or susp noise? It sounded like you were describing pre ign detonation. This happens when the engine has carbon buildup and/or wrong ign timing. Sometimes this also happens with a Honda/acura that takes prem. gas and someone runs regular. I would find out what type of noise it's making, engine or susp.