Why Couldn't Ron and Hermione Hear the Basilisk?

[Robert Jones]

No: HPFGUIDX 94664

COS explains that Harry could understand the Basilisk because he was 
a Parseltongue.  But why couldn't Ron and Hermione even *hear* it?  
Shouldn't it have made a hiss or some other snaky noise?  Nothing in 
the book suggests that a Parseltongue could read a snake's mind or 
had especially acute hearing — so shouldn't there have been some 
noise for Ron and Hermione to hear?