Popping & crackling during calls

[TerriC]

My phone has started making intermittent popping/crackling during phone calls, so that I constantly have to ask the person on the other end to repeat themselves. It happens when I put the phone on speaker, and also when I use my headphones, but it does NOT happen when I'm listening to music, so I'm completely confused.

I have a Sprint Samsung Galaxy S5. I appreciate any help you might be able to give me - thanks!