2000 Jeep Laredo loud noises under the hood (sounds like a

First, the rear door not locking but the rest of them do, tells me that it may be your door lock actuator is probably bad. To help you further on the noise under the hood, we need to know what kind of noise it is making. Is it a whining noise? A squeel? Does it make this noise all the time? A lot of those engines had issues with idler pulleys going bad after 100,000-160,000 miles or so and will make a squeeling/whining noise under the hood. Let us know what is going on so we may be able to narrow down what it could be. Also, which side of the engine is the noise coming from?

I would say it is more of a squeal and it seems to be coming from the passenger side of the engine towards the front belt/alternator. It is really only noticeable upon starting the car while it is in idle as well as if you stop at a light (in idle) again. I would say this started about 3,000 miles ago (at 127K) Sound like the idler pulley going bad? If so, any idea (estimate) on what parts and labor are to replace this?
Thanks for your help Beef99!

Withou actually being there, I would say that as long as you are not leaking coolant anywhere or anything, that your problem is your idler pulley. They cost around $25-$35 for the part and if you fix it yourself it would just cost your time. They are easy to replace and held by one bolt through the center and are 14mm or 15mm bolts. Make sure that you purchase one from a good auto parts store or a dealer or you will end up replacing it again in a year or so and do not overtighten the belt after you are done. If you have a garage do it, it could cost up to or more than $100 depending on where you go to have it fixed.