try to clean out your speaker on your phone with a damp rag . could be dust.

I tend to talk in the room where my router and modem are. I don't know if this has anything to do with it, but sometimes when I am using my phone, the person on the other end tells me there is a very loud noise-sounds like a train. I don't know if this is a T-mobile issue because it only happens sometimes. Your thoughts?