Hi Paul
I don't have the trv230, I have the trv320. I have noticed the same thing about grainy footage in low light conditions. I had to use a video light to improve things. There is no substitute for good lighting conditions unfortunately. You will have noticed that on bright sunny days the picture is extremely good.
You don't mention if you hae the camera dv-in enabled if you do then you can try and edit the footage on the pc to try a clear up the image then send the footage back out to tape. I have listed below the web site for ordering software(autopc95) to enable your camera for dv-in. it also actiates other functions listed below alll thisa for £40 what a bargain. The guys at the site are excellent lots of excellent advice.
Sony Digital 8: Analogue, S-Video, DV-IN, VTR/PLAYER RECORD, Manual White Balance &
AVin to DVout Passthrough (AV>DV Realtime Convertor) Menu modes are enabled on these cams:
TRV120e TRV125e TRV230 TRV235 TRV320e TRV325
TRV420e TRV430 TRV420e TRV530 TRV725e TR8000/8100e
http://www.lynxdv.com/dvstore/
Hope this is of some help, let me know if you need any more info.
The Duke