[TheBigNate]

I've had this strange "chirping" noise for around a year or so at this point. Car is a 2006 330i. It only occurs for a second when the engine and engine bay is hot. I posted about this problem before and was told it was probably a belt or a pulley making the noise. So, yesterday I finally got around to replacing the belt, tensioner, and the idler pulley with OE FCP Euro parts, and to my surprise, the chirping noise did not go away on a warm start. I followed by checking for visible wear on the alternator pulley and the power steering pump pulley. I began troubleshooting and realized that the noise can only really be heard from inside the cabin. I'm sort of stumped at this point and not sure where to continue looking from here. Below are videos of a warm start (the car was driven for about 20 minutes and then turned off prior).

https://1drv.ms/v/s!Ajz7oTgyZSpbp3NPUyBChajKH1f9 Inside cabin

https://1drv.ms/v/s!Ajz7oTgyZSpbrX6gajCwfYacLUfD Front of engine

https://1drv.ms/v/s!Ajz7oTgyZSpbrXgSSugPcXS85i0O On driver side wheel

https://1drv.ms/v/s!Ajz7oTgyZSpbrXrt6UetRiKGgnEp On passenger side wheel

https://1drv.ms/v/s!Ajz7oTgyZSpbrXnmSCkbphVodn1s Rear

[TheBigNate]

After about 5 more rounds of placing cameras everywhere to record the sound I found that I could not hear anything from the engine bay. It is loudest towards the drivers side footwell and the dashboard in general. Is there anything in or behind the dashboard in the cabin that could possibly make this chirping sound? Could the heater core, evaporator, or even the onboard computer possibly make this noise?

[opjose]

The CIC does have a fan.

[TheBigNate]

Update: Got it diagnosed by BMW and it turned out to be the vacuum pump for the brakes

BMW Mastertech said he’d never seen this problem before. Must be rare

[Kiemyster]

Do you know if it was it the pump itself or just the seal that failed?

[TheBigNate]

Originally Posted by Kiemyster

Do you know if it was it the pump itself or just the seal that failed?

I'm not entirely sure. The BMW Master tech I spoke with seemed confident after unplugging the vacuum hose and reproducing the sound on every start that there was an "internal fault" within the vacuum pump assembly. Even though it was more expensive to replace the pump instead of a seal I didn't want to take any chances with a daily driver. I was also getting 2 symptoms; the obvious chirping sound along with the "hard" brake pedal. I never noticed that the brake pedal was actually abnormally hard to press when performing a cold start but since the pump was replaced it has been very easy to press. In the end, I got it replaced at and indy for a reasonable price.

It's entirely possible that it was just a seal that went bad but I never noticed any oil leaks around the pump or anything of the sort. I decided I would just pay for the entire pump replacement for peace of mind.