Intermittant Blurry playback

[mobiusnz]

I'm having a problem with my Setup that intermittantly some of my recordings are blurry. It can't be a playback codec problem as they are blury played back on my MVP as well. I've attached a screenshot example. There seems to be no rhyme or reason to it. This recording was a 5am test match between Wales and NZ Allblacks so before I went to bed I checked things out - I set both tuners recording including the first tuner on the Sky Sport channel and played them both back and both were fine. I cancelled both recordings and set the 5am recording and lo and behold it was blurry. I've always had this problem but it used to be very rare - its happening a little more frequently now. My pc I record with is:

Shuttle SN95G5 ver 2.0
AMD Athlon 64 3200+
1 GB Ram
120GB Special Edition SATA Western Digital
Hauppauge WINTV 500MCE

I'm using the Cable setting rather than Antenna as otherwise I can't record Prime and Sky via my UHF decoder as the NZ tuner settings don't have the high frequencies - I understand theres a fix for this but I've always used the cable setting till now and generally don't like to change a winning recipe - allthough its not quite winning at present. I has happened on tv2, tv3 and Sky and I *THINK* with both tuners although sometimes its hard to be sure which tuner kicks in when taping many subsequent shows.

Anyone else had this - any ideas or thoughts? (P.S - Note the score - 34 - 3 Be VERY affraid Ireland/Scotland/Englang!!!!)