Kev999
Why use Freeze? Muting should be sufficient.

To enable the OP to continue working

Yeah, random and intermittent. Which makes it hard even to devise a strategy. But if I can determine that a certain synth is active during all the events, that would narrow it down I would think.
I'll try to run DP as administrator, though this is the first I've heard of that, and I have run it many times in the past. I'll probably end up reinstalling it.

I agree with Kev 999 that you should try freezing all your synth tracks.  Its quick and easy and may solve or help diagnose the problem.

BRainbow
I agree with Kev 999 that you should try freezing all your synth tracks...

 
That wasn't me. Freezing might actually mask the problem. If you freeze the synth that happens to be the one that is causing the hiss and it doesn't hiss during the freeze process, then you'll never know if that was the one. Also, freezing takes time whereas muting or soloing is one-click and instant.

I think he's taking about Quick Freeze which takes a couple of seconds.
 
If you play back afterwards and it doesn't hiss then you've kind of nailed it

I uninstalled and reinstalled Dim Pro last night, on the theory that perhaps Dim LE was the culprit. Also, I would rather have Dim Pro than LE anyway. That went fine, so far no noise. So I'm now using Dim Pro and have turned LE off. Until I get the noise again, that's my theory and I'm sticking to it. If it comes back, I'll continue troubleshooting, considering all the very helpful advice you folks have been giving me.
 
One thing I wonder about re: Dim Pro: I don't think I've ever got the DXI or 64-bit versions working. I always use the 32-bit version, which has always worked fine. Anyone have a different experience?

I never install 32 bit anything. I wonder why you couldn't get it to work? Are you using the 64 bit version of Sonar? 

I'm actually using the New CbB as folks have decided to call it. That's 64-bit only, isn't it?
 
Re: Dim Pro, id the noise returns, I plan to reinstall again, this time installing both 32 and 64 bit versions. I should have just installed the 64 last night along with the 32. Oh well, some good hockey games on tonight....

I'm with Cactus - I don't install anything 32 bit unless there is no alternative 64 bit version

If the noise comes back, just mute one track at a time until the noise goes away.
 
Then something on that last track muted or something it routes to,  is related to the noise.