Such noises are somewhat normal for a system with an expansion valve. The 124 has the TXV mounted more or less directly behind the tachometer, so the noise is perhaps more audible than on other models of car.

My experience is the sound becomes much louder when the car is low on refrigerant charge. Since the system was just serviced, do you know how much R134 was used to charge it? As well, perhaps the new expansion valve is simply more vocal than the old one, and it's a feature, not a bug...