Nissan X-Trail front end noise

Hi all, I have a 2001 model X-Trail & over the past few months it has developed an intermitant knocking noise in the front drive wheel area, it seems worse when turning right on round a bouts & goes away when I turn left & is intermitant on straight runs. I have had the wheel bearings looked at & was told they were fine & strangely enough the noise is mostly prominent in the mornings & as the day progresses & the car warms up it appears to go away until the next morning. I have had the local nissan agent look at it but sadly by the time I get there, the car has warmed up & "presto" no noise. They say if they can't hear it, they can't fix it.
Is there anybody out there that may have some suggestions because they all think I'm going batty.
Cheers Dennis