UPDATE: because the 945 was originally sold in California, it has the pulse air system. The sound is
from air being pumped into the exhaust manifold ports.

Thank you for the suggestion and instructions. I stopped by the Volvo service shop in Sacramento yesterday and played them the video of the noise. They were 99% sure the "knocking" noise was coming from the AC compressor.

I don't have a stethoscope but I will try some of the
"Tricks" for listening for noises. Can't wait for tomorrow
morning!

Thank you for the input. I have timed the noise now every day as it only does it when the engine is cold. It is exactly 1 minute and 28 seconds when the noise abruptly stops. The only thing that I can think of that functions this way would be the thermostat. Could the noise be related to the water ...

VID_20250811_101634811~2.mp4 The attached video captures an unusual sound at cold start that seems to activate after engines starts and then literally stops after approximately 1 minute and 28
Seconds every time. It only does this when the engine is cold. I have owned many Volvo in the past with ...