If you have a belt squeal, it might be this

Having a drive belt squeal, it was reccommended here that I replace the belt. Since the idler pulley was worn, I replaced it too.

However, it turned out that it was the harmonic balancer going bad and, if it does as it did in my case, it will leave you stranded. The harmonic balancer on my 99MGM is a three piece unit. The outer rim with the belt grooves actually seperated from the rest of the pulley and fell off. Fortunately, I was only pulling out from a parking space near my home when this happened.

I have not seen this problem mentioned in any of the posts here but, it seems that this is not that uncommon an occurance. As I odered the part from my local Lincoln Mercury dealer, I was told that there was another Mercury in the shop with the same problem.

The word of warning here is, if you replace the belt and idler pulley and you still have belt squeal, it could be the harmonic balancer going bad.