While running felt a "pop" in my achilles?

Ice it ,: See a foot/ankle specialist asap. Walk on your tippy toe if you had to walk. You may of ruptured the tendon, ......

Possible tear: This could be a partial tear of either your achillies tendon or a very small vestigial tendon which is next to the achillies called the "plantaris"tendon. To save money i would have a diagnostic ultrasound of the tendons performed and if inconclusive then possibly an MRI if symptomatic enough. Why don't you consider the use of an elliptical machine or nordic trak skier both give great cardio.

Partial tear: You may have injured or torn part of the achilles tendon or one of the three muscles that make up the tendon. If no residual pain, no worries.