My 2005 C230 is making an occasional popping-type noise with the A/C on while stopped or idling. It doesn't happen all the time and it can be heard only while the window is down. This happened last summer but A/C still worked. Two months ago while it was still cold outside, the alternator light came on and I lost power steering along with engine temperature rising. The diagnosis from a local mechanic was to replace the drive belt, belt tensioner, idler pulley and a coolant pipe that broke. Those repairs were evidently made I thought this may solve the A/C noise issue.

Yesterday when using A/C for the first time this spring, the noise happened while going through a drive-thru. I turned off the A/C and the noise stopped. After leaving the drive-thru and turning the A/C back on, the noise did not reappear, neither while driving or at a stop sign. This noise seems to randomly appear while idling or stopped, but isn't consistent.

Assuming the drive belt, which I believe is the serpentine belt, was replaced along with the other repairs made, I'm wondering what the issue could be. I'm also wondering if one or more of those parts I paid to replace weren't actually replaced. The closest Mercedes dealership to my home is about 65 miles away. Any ideas?