Beats sound off sync

OK... I have been a vinyl dj for 20 years and made the switch over to cdj's recently having purchased the 350 package.

Is it just me or are these faulty or am i missing something??

I beatmatch by using my ear without looking at the BPM counter and its seems ok for a while then the beats dont sound right,

for instance, whilst in the mix, 2 tracks are playing and it sounds great then i notice 1 beat is off like a clipping type of sound then it goes back to sounding ok then off again.

So 4 beats in a bar. the first 3 beats sound dead on then the 4th sounds off, the next bar sounds dead on but continues with this rogue beat being off sync. I have tried all different tracks and still the same when in the mix.

So i found 2 house tracks at 128 BPM exactly and played these together and had the same sound, it sounds really rubbish when i record a mix and listen back to it.

I never had this problem when using vinyl..

Anybody else had the issue??