Any one encountering a strange buzzing noise when recording a group of soft synths . It happens over say 16 bars and stays much like an unwanted reverb tail . Bizzare !!! 

Remove your plugins, try new ones. Then see what happens.
Narrow it down.
Cheers...

Ok will see 

Oh don't forget to RESET and rescan your plugins if you haven't already assuming you are running X3D.... cheers...

Sylenth - Big time !!! . As stated before its like a reverb sound that just builds and builds . Sylenth is 64 bit version -Strange . Never happened in X3c so I am baffled 
 

You have the latest version of their plugin? Any updates?

Yes all ok on that . Only happened since the update so ........

Try disabling/re-enabling 64 bit engine in Sonar preferences to see if it makes a difference.
Try enabling/disabling MIDI out for that plugin if it exists (right click the soft synth in the browser).
Create a brand new project in X3D. See if you can reproduce the issue again.
 
Otherwise I'm thinking you will have to contact these guys:
http://www.lennardigital.com/modules/sylenth1/
 
Other Sylenth users might want to chirp in and try and reproduce.
 

Thanks - done all asked ! Going to contact Sylenth 

Thanks keep us updated...