Low speaker and caller not being le to hear due to crackling noise

Bought my Dad one of these second hand last week. Made a phone call on it and it was perfect. However my Dad has taken the phone and now he's having too issues with it. He says the earpiece is too low and he can't hear anyone, also when he rings other people there is a loud crackling noise, it sounds like there is wind blowing into the phone. When he turned off the phone and replaced the SIM card it was okay for awhile Is this a SIM card issue, network issue or a phone issue, I'm super confused here.