2008 bought used. Has ~140K miles. The AC compressor made the dreaded squeal again last night. This will be the 3rd compressor in 4 years. Why does this keep happening? Any ideas? Taking this to a trusted mechanic that we have known for years, have followed from one shop to his new shop. Something is being missed. Also, seems to happen after the expy has been sitting for a while with the AC running. Last night we were sitting about 20-30 minutes. Thank you.