Go buy the brake bleeding kit from Harbor Freight. It's like $15 and you can diagnose yourself. Also, it's very easy to pull the IWE vacuum line off of the IWE (good idea to plug it). With it disconnected the IWE engages (and noise should go away). You should be able to test each side for noise. Note that the vacuum pressure keeps you in two wheel drive. Lack of pressure engages the front wheels, so too LITTLE pressure, like a leak, can cause partial engagement which is why you hear rattling (and you'll wear stuff our very quick).
After a BUNCH of IWE problems and ruling out the viability of the IWE eliminator kit (that argument is for a different thread) I went with the RCV IWE upgraded rings and have had no more problems. Though, I agree to use your warranty for this while you can - I did multiple times.
That being said, once you replace the IWE yourself you'll learn it's less terrible than you might think, and they aren't very expensive. I carry spares now and could do a trail swap. I encourage you to replace one when you get a chance. It's really handy to know how - plus you can play with the thing and understand it all. It's pretty simple (and terrible).
