Iphone 5 static sound issue when calling

hello, i having this very werid issue.

when charging my phone, i will have this static or popping sound when making calls but when i switch it to speaker or using earphones it doesnt have anymore.

when my phone is charged up to 100%, i will have this same issue of static sounds during calls until i used the battery up to about 85% where it doesnt have anymore. as the battery percentage drops, the static sound get lesser and lesser.

is anyone having the same issue as me???