There are two possible causes.
1. Have you connected an analog player with a built-in phono equalizer? Connect the analog player with built-in phono equalizer to the [CD/LINE] terminals. If the analog player with built-in phono equalizer has a PHONO/LINE selector switch, switch it to PHONO.
2. Is a USB sound card (audio interface) for a computer connected between the analog player and this unit? If the output of the audio interface for computers is line level, connect it to the [CD/LINE] terminals. If the analog player has a PHONO/LINE selector switch, switch it to PHONO.