Its not that hard to take the seat apart. remove it from the vehicle, At the bottom of the seat back there is a clip running the length of the fabric. That clip locks the fabric front and back together. Unclip it, find the 3 bolts for the upper half, 2 on one side one on the other. The side that has two bolts, the bolts will be located under the fabric up away from the bottom. Unbolt them. Locate any upper seat wiring running through the base and remove it with the upper half.
After the upper is separated you can peal back the fabric far enough to work on the lumbar device. There is a large plastic shield on the seat back frame that you can unclip and move out of the way. That is essentially a piece of spring steel on two guide rods. The spring steel flexes when the lumbar is raised using a cable hooked to a crank in the base or a motor in the top. You should be able to locate and silence your noise at that point.
If your seat has a built in air bag the ability to remove the upholstery is more limited however you can still pull it up enough to get to the lumbar.