Dear Pros, thanks for all the advices. Yes, the spray bar does make high-pitch noise, but I removed the spray already, the loud low-frequency noise is from the motor. I just got a Fluval 304 from Petco, this one is very quiet, I could only hear slight motor noise by placing my ear close to the filter. I am going to exchange for another XP3, see if the new one improves, and do an update later. Thanks.