Bottom of heel pops when go onto tiptoe.feels like strumming of harp strings, followed by cold tingling sensation in heel & ankle. what can this be?

Tendon displacement.: Several of the tendons crossing the ankle joint can be displaced out of there usual track. You could have an injury to the Achilles tendon. You need to be examined by an orthopedic surgeon. Achilles tendon injuries can go on to rupture and require surgery. Don't put off evaluation.

Cord or Chord ??: The cold, tingling sensation of the heel and ankle is be caused by a temporary disruption of normal nerve impulses in a rather substantial nerve supplying the heel and ankle. The cause is no doubt from the harp string strumming and popping of one or more of the various, rather robust soft tissue elements located in that area of the foot. Start the evaluation by a seeing a specialist of foot/ankle.