Yes, the big deal with contactors is that they're designed to switch high-current inductive loads. Smaller relays may have problems with the arcing caused by a

Yes, the big deal with contactors is that they're designed to switch high-current inductive loads. Smaller relays may have problems with the arcing caused by a load like a motor welding the contacts together. So, they have bigger contacts to handle the current and strong springs and a powerful solenoid to open/close the contacts quickly and extinguish an arc before it has time to melt anything. The noise you're hearing is from the contacts opening and closing.