Need help on crackling sound on my amp

[al89]

I have a vox cc2 amp. Recently there is a crackling sound coming out of it. I am sure and checked that it isn't the input jack of the amp. So I am wondering could it be the cause of the tubes life that has worn out or the speakers are damaged. Can any one help me with this? And if the speakers are damaged all I need to do is to swap out the cabs? Any advise? Thanks!