Cubase LE 5 Crackles when monitoring

Hi everyone,
I’ve been having a sporadic problem with cubase that causes me to hear crackles when
listening back to audio that i’ve recorded.
The audio has no crackles when i listen to it on windows media player etc.
I thought it may be a latency issue but i’ve adjusted it to it’s laziest point (1024 on my MOTU ultralite hybrid)
I’m really at my wits end as i’ve struggled with similar problems for the last goodness knows how many years with
cubase/nuendo etc.
I previously used a Lexicon Alpha , which had the same problem, and could be solved by fiddling around with settings/turning on and off etc then it would go away.
Any ideas/advice would be greatly appreciated.

Philip Morris

System specs please…

I’ve got an HP G62 laptop I5 with 4mb RAM & a MOTU ultralite hybrid.
I changed the settings on the project that i encountered this problem on from 44.1/16
to 48/24 and the crackles disappeared, presumably when cubase redid the files at the new
rate, no idea why it would be a problem before…