After my recent upgrade to 13.04 I am experiencing background crackling noises, particularly noticeable when using my preferred listening over headphones (Grado SR80's). The noise is only evident when audio is playing from any source (Banshee, Clementine, DVD drive, Chromium eg You Tube). As soon as music stops so does the crackle. The noise may best be likened to the crackle I used to get as background when listening to vinyl records over headphone. Otherwise the quality of audio is unimpaired.
I usually use the headphones via a Asus Xonar U3 usb soundcard/headphone amp but the crackle is also evident when using my laptop's inbuilt headphone jack outlet.
The problem was certainly not evident before the upgrade i.e. when using 12.04 or 12.10.
My laptop is dual boot and the problem is not apparent under Windows 7 (although I much prefer the Linux environment, current sound issues aside). This would appear to point to a Ubuntu sound issue.
Any suggestions how this may be resolved?