2006 Mustang 4.0L Lifter noise

My Mustang started making a lot of noise the last month or two when I started it and when it’s been running awhile. I took it to the dealer since it’s still under warranty. the service dept. said it was noisy lifters and that was normal. I think they are wrong about it being normal since it didn’t do it when I bought the vehicle. Has anyone else experienced this or can anyone tell me if this is normal.