The old adage- if it ain't broke, don't fix it. A/C compressors age like all car parts do. And noise sometimes indicates that age. Because a/c compressors are expensive to replace, its best to wait until either A. the noise becomes horrendous and untolerable, or B. the compressor fails to operate. On the other hand, if you have the funds now to replace the compressor, and the noise bugs you, get it done.