I just purchased 2 more PSI Air filter AC620 and got them installed and noticed they were noisy. I then went over to my other one and it was just as noisy. I open each one up and found a little black box mounted on the blower cage was the problem. I opened up the box and inside it was a capacitor just laying in there. I spoke with PSI support and they also opened it up and their capacitor had the wire wrapped around it. So I decided put some calk/glue on the capacitor and also a wire tie which I had to drill holes in the black box to hold it in place until the glue harden. All three are a lot quieter now. The funny thing is when they were on the floor I didn't notice the noise until I installed them. To see if you had this problem just removed the filters, turn the blow on fully speed, and put you had on the black box to feel if it's vibrating. Also to do this you have to remove the complete blower panel assembly (10 screws). This will also give you a chance to clean it out real good and I still found packing peanuts in the blower cage.