You (often) don't know what parts were replaced before you purchased the car. Perhaps a single control arm & bushing were done previously due to a collision, off-road incident or monster pothole. It's a good idea to do them both at the same time. If they're original they're the same age/mileage. The outer shoulder of the road is more likely in bad shape vs. the inside lane, so passenger side components can be more worn. Our pampered one-owner 328i exhibited worn front lower control arm bushings at 40k miles.
Is it the bushing or ball joint that's making noise? Are the sway bar links tight? They often transmit noise when loose.
2006 330ci ZHP - Silbergrau Metallic / Stoff Laser/Anthrazit / Alu Black Cube trim / Adaptive Xenon headlights / HK hi-fi system / heated front seats