Maybe the calfs are just generally overused, and unable to totally relax during resting.

Try pressing down hard on the calfs and all the way down to right next to the achilles tendon. If you only feel normal muscle aches, not anything like localised soft tissue mass (or anything that makes you feel it may be serious), I guess you could try massaging deeply. I feel it helps me a lot, concentrate on the lower third either side of the achilles tendon, and upper third of the calf on the medial area where the belly of calf muscle locate. (*Remember to use lotion. You could learn some simple massage technique from youtube)

If that doesn't work, it would probably be wise to let a physio to look at it..... even if it's just to make sure there isnt anything require proper treatment.