I am really surprised that nobody else has given you a response, as most everybody I've met here has been more then quite respectable. If this is your first post, I hope that you don't have a bad impression.

The first thing you need to determine is the condition of your belt driven bearings and accessories. One of the best ways to do that is not visually, but audibly. You already know that there is a strange new noise, and now you need to determine where the noise is coming from. There are two easy ways to do just this. One way is to use an instrument to listen only to a specific component, this can be as simple as putting a tube or a screwdriver in your ear and touching the other end to various suspicious parts, the other nosies of the engine can then be filtered out. Another way to isolate the noise is to operate only the suspected device. For example, if you remove the belts from your accessories, your hand can operate each pulley independent of the others, thereby inducing the noise.

Nosies are very good indications of the health of reciprocating assemblies. There are in fact instruments called "Sound Velocity Meters". As the velocity of sound emanations are a function of the reliability of a machine, technicians at places like assembly plants can use them to predict failures before the machine breaks down. The techs can schedule a repair before the unit interrupts production.

If you are new to the Brickboard M, I hope that the lack of a response has not made you indignant.

Good Luck, and a very Merry Christmas to you and your family!!!!