All working but sound howling (slower-faster)!!!

Hello guys,
I have Mixvibes DVS 7.010 version and last update for U46DJ Soundcard 1.039. I tried with soundcard version 1.034 but the same problem. I have signal, calibration ok, and all working..only sound sometimes like goin' little bit down and up, like howling in some moments, slower-faster in some miliseconds.. You know like you mixing with normal vinils and when you move with hand record and she start goin' faster and is sound different to up or to down if you stop her little bit..so sound is like that on my mixvibes...
So is hard mixing because speed sometimes is moved and fucked up therefore that. Is especialy hard if you are in the mix..
Latency is on 256, I tried with other ones but same situation, so probably is not problem in that..
I have HP 6720s core duo on (T2410) 2.0 mhz with 1 GB ram
Do you know what could be a problem? I using Numark Cartridges CS-1, is maybe problem in cartridge? But I'm not sure..please help, thnx in advance.

I have Mixvibes DVS 7.010 version and last update for U46DJ Soundcard 1.039. I tried with soundcard version 1.034 but the same problem. I have signal, calibration ok, and all working..only sound sometimes like goin' little bit down and up, like howling in some moments, slower-faster in some miliseconds.. You know like you mixing with normal vinils and when you move with hand record and she start goin' faster and is sound different to up or to down if you stop her little bit..so sound is like that on my mixvibes...
So is hard mixing because speed sometimes is moved and fucked up therefore that. Is especialy hard if you are in the mix..
Latency is on 256, I tried with other ones but same situation, so probably is not problem in that..
I have HP 6720s core duo on (T2410) 2.0 mhz with 1 GB ram
Do you know what could be a problem? I using Numark Cartridges CS-1, is maybe problem in cartridge? But I'm not sure..please help, thnx in advance.
