amk1

Hello all,
I got a 991.2 C4S a couple of months ago. Since I got it, I have noticed this intermittent high pitched whistle noise from the air conditioning ducts although even closing the ducts one at a time hasn’t stopped the noise. It doesn’t happen on every drive; the intensity of the noise is variable; and today I noticed that it does seem to stop when the car engages in auto-stop in regular drive mode. Video is attached here (you can hear it go away toward the end)— thanks for any theories. I checked my coolant level in the back and it was near empty but the dealership said that wouldn’t cause this as long as the low coolant level light wasn’t on (had seen other threads discussing this as one possibility).

duxsi

This?

https://rennlist.com/forums/991/9310...on-normal.html

CSK 911 C4S

Does the whistle change pitch with HVAC fan speed?

Have you checked both filters to see if they are seated correctly or if they need to be changed?

amk1

It doesn't change pitch with different fan speeds, although when the AC is off, it is no longer present. I had the dealership do a full AC system check and they found nothing. Not sure what it is.