I have been using my crack + HD 650 combo for about a year, but I have always had issues with frequent weird crackling noises. Following several troubleshooting steps, I tried checking for soldering connections, etc. without any improvement. Abt 6 months ago, I upgraded to the speedball kit, and the issues still persisted with no change.
Turns out I had coiled up my headphone cable for convenience since the stock cable on the 650 is quite long, and my guess is it was acting like an antenna amplifying some signals in the office (computer, phone, etc.). In any case, simply undoing the coiling has removed almost all of the random crackling. I'll still get an occasional one if the cell phone is too close or something, but not nearly annoying as before.
Hope this helps someone who is in a similar situation as I am.
