"is it normal that my boyfriend cracks while he exercises?"

For his extremely late New Years resolution, my boyfriend Brian decided to start exercising. He got this P90X DVD set and started going into "X" version instead of taking it slow.

Anyway, he's about a week and a half into it and I would pass the room a few times and hear cracking, you know, like when you crack your knuckles or pop your back when you stretch. I asked him about and he would just say something along the lines or his age and needed an oil change as a joke.

I know he was spouting BS when he said that because he's only 18 years old. Why would he have a problem with his joints at that age? So I pushed it aside just this once and let him continue.

Right now, he's been doing for three weeks and I hoped he got into the swing of things and stopped making those noises. Unfortunately, his arms still pop when he lifts the weights or does push-ups.

It's been three whole weeks and I'm getting worried. I thought his body would be used to the program but those popping sounds aren't very convincing. Am I paranoid? Are these cracking and popping sounds normal? Or should I call both of his Dad to make him stop and rethink his exercise methods?