Q: Rat under Hood.

Of course, you want to be sure that the noise is really from the serpentine belt and/or connected rotating elements. If you simply take all of the belt driven accessories out of the picture by removing the drive belt and then briefly run the engine that will provide confirmation. If the noise does disappear with the belt removed, it may be that certain pulleys were not replaced and/or the noise could be coming from defective bearings in a driven accessory such as the A/C compressor or the alternator. An additional thing to check is whether all of the pulleys are in the same plane. For example, if the crankshaft pulley on the harmonic balancer is out of position, the serpentine belt will not run straight, possibly causing noise. If you want these steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request serpentine belt noise diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.