I think I may have the same issue. I get a strange sound that seems like the AC belt is slipping. I can replicate the sound in the garage by holding the rpm's at about 2500 and turning the AC on. It seems that when the compressor kicks in the belt slips a little and makes that noise. It only started happening after I replaced the AC belt.
That being said, this is only my personal diagnosis of the problem. If you could take it to a dealership and have them look at, determine the problem, and then report back here, that would be a huge help. I've been thinking about getting a new AC belt to hopefully cure the problem, but I'd rather know specifically what is wrong before just throwing money at the problem.
In closing, I'm pretty sure that it's just an issue with the AC belt itself. I say that because I never had this problem with the stock belt. It only started happening after I changed the belt.
Please let me know if you find out anything. Thanks.
P.S. To actually answer your question (sorry for my ramblings on), yes this is absolutely something that should be fixed under warranty. Get that thing to a dealership on Monday morning and make an appointment. If they can't get you in right away, make sure you let them know that you're close to your 36,000 mile mark and that you want the problem fixed under warranty. Have a tech check the odometer that day. That way if it goes over 36K before they get you in, you'll still be set.