I'm training for a half marathon and noticed when I get up in the morning I have a "clicking" in my right Achilles' tendon. It's painless. Any ideas?

Tendon catching. This may be coming from the peroneal tendons but radiates to the achilles. Sometimes there is a peroneal subluxation which can create a clicking sound as the tendon passes around the ankle bone. If it is truly coming from the Achilles tendon, there may be a nonpainful bursitis creating this clicking sound.