If theres no pain, I wouldnt worry too much. My body makes all kind of twanging, crunching, grinding type noises on my warmup sets, it doesnt bother me anymore.

If I remember correctly, the fluid in your joints (synovial fluid, I think) heats up as you warm up, and it acts on your joints like oil does in a car. As it gets warmer, it gets thinner and more liquid-esque, but until then, your joints might make funny noises.