What's the difference between the following examples:

> 
> 1. I noticed that the clock **had** stopped.
> 2. I noticed that the clock **has** stopped.
> 
> 
> 

Some of them say that if the emphasis is laid on the subordinate clause then present perfect tense can be used, while some say if the emphasis is laid on 'noticing' then past perfect tense is to be used. How correct is this explanation?