Has anybody had an issue like this?
 
I have a project I started in X1 but I'm mixing it in X2. It's only about 30 tracks, most of them frozen midi tracks (sd3, Kontakt, Dim Pro), and not that many plugs. Whenever I make any changes at all to the project, even something as minor as a volume change on a track, when I play the project I have a tone, like a test tone or something, that plays in the background. If I close the project then reopen it everything is fine but as soon as I make another change the tone is back.
 
Another thing; this is the first project I've worked on in X2, I haven't started a new project yet, and my cpu meters are waaaaay up there, like almost into the red zone. Is X2 that much more of a resource hog? This same project never got anywhere close to that in X1. My computer isonly about a year old, quad core @3 ghz with 16 gigs of ram, seems like it shouldn't be straining like this on such a small project

Only thing I can think of is a soft synth is getting a MIDI on note from somewhere and no MIDI off note. What happens if you click on the MIDI reset icon in the transport bar?

Another possibility is a demo plugin that will not allow you to save changes or has bypassed its demo expiry time.

Either way, you should not be seeing cpu meters being "pegged" on your system.

You need to start doing some diagnostics

start by running DPC latency checker

http://www.thesycon.de/deu/latency_check.shtml

FBB- All the midi tracks are frozen. I even tried archiving the tracks with midi themselves but it didn't help.

lorneyb2- I don't have any demo plugs installed, all the plugs are Cakewalk plugs included in X2.

Jonesy- Good idea, I haven't run DPC latency checker with the project open, I'll try that today, see if I can isolate anything.

Thanks for your replies, guys, really appreciate it. I'm sure I'll find in the end it's something simple I've overlooked.