Heavy crakling on bass amp! Help plz!

[Marcwild]

The problem is that the sound of my bass is perfect i can play without problem, But sometime not each time some crackling very loud sound from my bass amp! If i play or not this crackling is here! I can deplug my bass and all other wire except power and put the volume down and the crackling is still very loud this change noting! The crackling is like POC POC POC POC POC CRACK CRACK CRACK! But if the crackling happen when i play bass the sound is perfect! Except this crackling WHO NOT AFFECT THE BASS SOUND! But the crackling is more loud than my amp sound! So... I check inside my bass amp! All look good! I check all wire, almost everything all look to be fine! (don't worry i have some electronic lesson at school) I was thinking it was the Stereo media input cause if i plug something inside this remove the crackling... So i remove this part ( i never use it i an i know i should not do that!) But this change nothing the crackling is still here! I was thinking it was some parasite signal but not! I try it to my friend house and the problem is still here! So i would like to have your opinions about this problem...