First, my specs: Win 7 64-bit, 2500K i5, EVGA GTX 570 OC (Hooked up to HDTV and Monitor), 8GB DDR3, Corsair 750W PSU, 2TB 7200 RPM WD Black.
I'm not sure when this issue started occurring - it may have happened since I built my PC in September - but when I play most games view movies/TV from my computer there will be a slight stutter on my HDTV.
For example, in both Portal 2 and Diablo III I have V-sync on and I notice a slight hiccup every 4 seconds. I opened up FRAPS and it'll stay at 60 FPS for 4 seconds then go to 58 FPS then 1 second later go back to 60. With V-Sync off, it'll do something similar as well, jumping from 150 FPS to like, 148 FPS. It doesn't "sound" bad but when your running in a game it's very noticeable and annoying.
This also happens when I watch movies and shows, on any video player. It'll go from 24 FPS to 23 FPS every 4 seconds, making most of them unwatchable due to the almost-constant jerkiness.
I know a workaround to the issue, but I'd like to not have to do it. If I unplug the cable to my monitor, my HDTV will stay at 60 FPS with no stutter at all. It sucks having to pull my computer out and unplug the monitor cable, though.
Note that if I play a game on my monitor (with both displays plugged in) I don't get the stuttering issue. I've also tried playing around with some settings of the NVIDIA Control Panel but it didn't help. I also tried switching the ports around and changing cables for the GTX 570, but that was a no-go. I've also tried updating the NVIDIA drivers.
Edit: Just noticed that if I put the HDTV as my Primary screen and leave extended on then I don't get the issue... But if I make it primary and put it on Projector only (HDTV), the issue occurs still. Still an annoyance cause with it on Primary then I can't really use extended displays too well because the task bar is on the HDTV then. Hmm...
Edit 2: Uninstalled and reinstalled the NVIDIA software and drivers, but that didn't fix the problem. I give up. :\
I reformatted my HardDrive a month ago to start fresh and hopefully get rid of the problem. It actually did. But I noticed now it's doing it again, and I don't know when it started. I would do a system restore, but unfortunately the earliest restore point only goes back 6 days. I've installed a bunch of stuff since I reformatted so I don't know if there is any application or driver in general making this happen. I haven't updated the NVIDIA drivers since I reformatted, so I know that an update didn't break em.