Jittery Video & Audio

I hope somebody else has had this problem and fixed it.
When I play video or audio from a WHS2011 network share on my Win7 or XP machines the video file keeps halting like it is buffering.
the files usually play for several minutes without issue and then freeze for a few seconds and then continue on for a few more minutes.

If I just drag the same video file from the WHS2011 network share onto either of my PC's the transfer rate is around 50MB/s on our gigabit LAN and the files play fine locally on either of those machines.

If I try and access the same video via DLNA on my Conceptronic Media Titan the same files work and stream fine.

I tried accessing media on several different drives on the server in case it was a HDD problem, no change.

I have rebuit the WHS2011 box twice with the same problems.
All drivers are showing up as working no network errors are showing up.

If I switch back to WHSv1 I can access the same files just fine on my Win7 & WinXP machines.

Hardware for the WHS2011 machine is
2.4ghz Dual Core E3200 Celeron
2GB DDR2
Samsung 1.5TB System Drive
1 x Samsung 1.5TB Storage drive
4 x 2TB Samsung Storage drives.
Gigabyte MB
PSU Corsair HX650