TVservice.exe strange CPU load (1 Viewer)

[Xaoc]

MediaPortal Version: 1.1.3
MediaPortal Skin: blue3wide
Windows Version: Windows 7 SP1 32bit
CPU Type: Intel(R) Atom(TM) CPU 330 @ 1.60GHz
HDD: Seagete 2.5" 40gb
Memory: 2Gb DDRII
Motherboard: NVIDIA ION
Video Card: NVIDIA ION
Video Card Driver: 266.58
Sound Card: NVIDIA ION
Sound Card AC3:
Sound Card Driver:
1. TV Card: Prof 7500 USB
1. TV Card Type: DBV-S
1. TV Card Driver: 2.0.0.2
2. TV Card:
2. TV Card Type:
2. TV Card Driver:
3. TV Card:
3. TV Card Type:
3. TV Card Driver:
4. TV Card:
4. TV Card Type:
4. TV Card Driver:
MPEG2 Video Codec: Microsoft DTV-DVD
MPEG2 Audio Codec: Microsoft DTV-DVD
h.264 Video Codec: Microsoft DTV-DVD
Satelite/CableTV Provider: Amos/Sirius/Hotbird/Eutelsat w4 w7
HTPC Case: Asus Eb1012
Cooling:
Power Supply:
Remote:
TV: LG
TV - HTPC Connection: HDMI

I have a strange problem with Tvservice.exe process, when i start LiveTV on a SD channel TVservice.exe loads CPU for 30-50% but after feaw minutes(3-4) it loads CPU for only 10-15% if i dont change the channel, if i switch to another SD channel it loads CPU for 40-50% again, and after 3-4 minutes it loads CPU only for 10-15% The screen and sound are normal all the time, but If i switch to HD channel TVservice.exe uses 45-50% CPU for 3-4 minutes and after this time the load is 25% but video and sound lags all the time.
All this time Mediaportal.exe uses only 5-10% of CPU, can somebody tell me whats the problem