I opened the book and began reading

[alpacinou]

Is this correct?

I opened the book and began reading when the faint moans of my downstairs neighbor's lovemaking seeped through the floor, distracting me.

Is it okay to use "seep" for sound?

 

[Tarheel]

Yes.

 

[emsr2d2]

Starting with the past simple suggests that you waited until you heard the moans before opening the book. I think you mean something like:

I had just opened the book and started to read when the faint moans ...
No sooner had I opened the book and started reading than the faint moans ...

 

[jutfrank]

Is it okay to use "seep" for sound?

At your level, you can be as creative with the language as you wish, so it isn't a question of what's 'okay' as much as a question of what's good writing. For me, it's not a very good metaphor. Think about what other things normally seep.

 

[tedmc]

It's a matter of the choice of words. Liquids seep (slow process), but sound penetrates.