Hi everyone,

My IS350 is currently at about 114K miles. Around 2,000 miles ago, I started noticing a faint clicking/rattling noise when the car was parked with the A/C on for a while. It was pretty subtle and intermittent and immediately stopped as soon as I turned off the A/C, so I assumed it was just the A/C compressor.

A couple of months back, I noticed a rattle at the top of redline, it only happened right when I hit redline and disappeared immediately after shifting. Today, I also started hearing a similar rattle during hard acceleration around 3–4K RPM. This one seems to be coming from the front passenger side of the car, which is what’s confusing me, since from my understanding the A/C compressor is located on the lower driver’s side.

My first thought was that another pulley might be starting to go, but that doesn't fully make sense since the original noise only happened with the A/C on. I’m also wondering if it could be something like a loose heat shield, are there any common ones on these cars that tend to rattle over time?

It still could be a pulley or accessory component, but I haven’t had a chance to properly inspect it yet. In the meantime, has anyone experienced something similar or have any ideas on what this might be?