Strange noise when running A/C on a hot day

[Tieniber]

Hi everyone,

On very hot days (95+ degrees), with the A/C cranking, I sometimes get a very strange noise coming from my '99 Boxster. It only happens when I drop the engine out of gear and down to idle, and it sounds like a loud version of when you run your finger around a crystal wine glass. It doesn't happen every time, and doesn't last for a consistent amount of time (anywhere from 1/8 second to 2 seconds). Since it's such a strange resonating sound, I cannot tell where it's coming from, but it sounds like it's towards the front of the car.

The only thread I found on the matter was someone looking to buy a Boxster and heard the same noise:

Used Boxster

Any ideas? Thanks in advance!

[newBgeek]

The noise is likely coming from the expansion valve. It's located under the front hood next to the battery compartment. Remove the lid for the battery compartment, then remove the cover on the passenger (right) side of vehicle. You'll see a small rectangular expansion valve. Put a screwdriver on it then put your ear on the screwdriver to verify the noise.

Mine made a noise too but it's lessened after running the A/C non-stop for several hours. I guess the previous owner didn't use the A/C much so all the seals dried out.

[Tieniber]

Interesting - I'll take a look. Thanks!