It's hard to say tho...
My old SuperReverb had a rattle that I couldn't find for 10 years. I noticed it when I bought it and figured I could get rid of it but nothing worked.
Then I forgot about it and didn't notice it anymore.
Ten years later I went to sell it and one guy showed up at my house who'd happened to hear me play at some gigs in town.
He said "oh.. that's the amp that has that really annoying rattle in it".

Suprised the crap outa me cause I didn't even notice it anymore.

Far as I could figure is that it was something in the construction of the actual wood casing. Like a bad joint or something.