Waveforms jumpy when scratching

This a new problem I noticed last week while at a gig and it happened again last night. The first time I was using technics and last night I was using cdj's...When I scratch the waveforms start lagging and getting jumpy...the audio isn't effected but the waveforms are majorly effected...

I have a Macbook Pro thats about a year old, all my music is on my external and i only use this laptop for djing so it really shouldn't be a memory issue or an issue with the computer not having minimum requirements...

The latency was set to 3 when the issue first happened...i tried changing the latency to various different levels to see if it helped and it didn't help

What are your computer specs and how full are your harddrives?

Macbook Pro, 2.6 GHz Intel Core 2 Duo, 4 GB 667 MHz DDR2 SDRAM...

My harddrive on the macbook is almost empty, I have all my music on a Lacie 500 GB external which is a little over half full

Try not using the external HD and see if this helps. It could be a performance issue with the external drive itself. Or maybe it was getting too hot and overworked those specific night or at that specific gig.