hi, we have vf6 1995 model in the shop. All was running well till this morning. Soon we started running the spindle, a high-pitched noise started coming. It is very consistent and comes in both, high and low gear. I do not think it is grinding but that is just me. Can someone help me find the problem? Should we keep running it? We are not having any vibration on the tool or on the machined part. Just the noise.