hmm. It seems like you'll have to do some experimenting and use the process of elimination. It's really unlikely that it's the H9 but you can eliminate that possibility if you have another piece of gear that you can use in the effects loop instead of the H9. Can you try a different power supply or try the power in some other place? Does the amp have a 'ground lift'? Here's a link that might shed some light on the problem. http://www.guitarworld.com/how-eliminate-guitar-buzz?page=0,1
