I own a 2006 Nissan 350z. I noticed the old belt was worn so I replaced it. After replacing it and tightening as tight as the old one was before, it started to squeak every so often. Thanks to some help, I found out it was the alternator’s bearing and replaced the alternator and the squeaking stopped.
As soon as it dropped to below 50 degrees, the car starts constantly squeaking again. It would go away eventually and come back. I’ve noticed that turning on the A/C, rolling down the windows and very rarely, turning on the headlights would make it squeak.
On warmer days when it’s 60+, it would rarely squeak. Sometimes it would squeak on start up and other times it would squeak 1 minute into driving.
Every time it squeaks, the voltage would drop to 12 volts.
It certainly looks like there are two serpentine belts on that car. I would try adjusting the tensions to see if the squeaking stops. Most likely the alternator belt slips since your voltage drops when the intermittent squeaking occurs and electrical load seems to cause it. Maybe the old belt was slightly stretched and the new one isn't quite tight enough? Hopefully there isn't a problem with the replacement alternator. Maybe this dude will be of some help. Good luck.
