My 2002 Mazda Tribute ES V6 recently started screaming and whining at acceleration. It used to just scream really loud in first gear while accelerating hard. Now it whines and/or screams in any gear while accelerating at any rate intermittently. Some days it's fine and it doesn't do it. Some days it is completely non stop. It makes the car sound like crap and you get looks from all around...

First off, I wish I could know if this is a safety hazard. Secondly i wish I could know what it is so I can get it fixed! My mechanic has no clue what it is. He says it's not the belt. He says he thinks it may be a bearing somewhere in the engine. But he says we have to wait for it to get worse to find it. But with the problem not getting any worse (at least for now) I'm stuck with something, potential dangerous screaming underneath my hood. Does anyone have any idea what this is? Should I get a second opinion on my mechanics theory that it isn't the belt?