I'm trying to buy an Epiphone Viola Bass (the Hofner Beatle Bass imitation). But the pitch on the Epi Viola basses I've tried drifts considerably when I play the open E (or low notes up to about G at 3rd position), oscillating between flat, sharp, on pitch, sharp, flat, etc, a bit like tape warble. (This happens regardless of right hand technique.) Other than this, I like the bass, though I'm not interested in it if the problem is unfixable. Is there a way to cure this pitch warble problem or should I move on to another bass?