VTSi's output sound crackling and popping in Cubase SX1

[owen22]

Hi,

Recently bought a macbook (2Ghz, 1Gb RAM, Snow Leopard) for music production and bought a secondhand copy of Cubase SX1.

When I use VSTi's the output sound crackles and pops and I just wondered whether it was a case of:

1) Not enough RAM (I only have 1Gb installed though I'm in the process of upgrading to 4Gb)
2) Compatibility issues between SX1 & Snow Leopard
3) Both of the above

Any ideas?

Thanks.