If the noise is heard when you are engaging the clutch then it's probably related to the clutch, or the clutch mechanism itself. It could also be something weird like worn fluid in the trans. Possibilities include a worn clutch disc, some type of contamination on the disc, lack of lubrication on the shift fork, or if the car has a hydraulic clutch there could be an issue with the master or slave cylinder. Depending upon what's found it could be expensive (clutch replacement) or not (lube the clutch fork). The best thing to do is to find a good technician to diagnose the problem and give you the facts.