aeroplane sound or alternator whine is from some sort of grounding problem, which could come from any wire in yoursystem, could be amp ground, player ground, rca ground, etc etc.....

easiest could be loose rca, difficult would be amp grounding to chassis not good, have to re-do, but worst problem of all, cant find the problem, haha.... sometimes rca terminal in amp or player ground solder loose, sometimes player need to add one more grounding wire, sometimes passive crossover too close to car ECU, sometimes speaker wire or rca wire too close to power cables, many many reasons lah....