My throw out bearing has been howling since I bought it. And the previous owner not knowing much about cars said that noise has been there for a long time. TOB 99% of the time only squeal because they are dry. Alot of mechanics seem to think they dont need to grease the bearing. Lithium grease(wheel bearing grease) should always be used. The only reason I havent replaced mine is because Im waiting so I can do the whole clutch at the same time. Ill put money on it when I put that clutch in there and I grease that bearing Ill never have a squeal again. Edit- One thing also to prevent noise is to try a steel retainer. With little lithium grease also, I think this may help with future squeals.