Hey man I'm just responding to your POD HD500 problems in that one thread. I am trying to rack my brain to figure out why yours could be hissing, but the only answers I have are 1) bad connection and 2) bad settings. Make sure that the connections are as follows:
Guitar -> POD Guitar in -> POD FX Send -> Amp guitar input -> Amp FX Send -> Pod FX return -> POD Line out -> Amp FX return.
As far as the settings, I can upload a patch with my settings so you can compare (heck, keep it if it works for you!). Maybe there's an answer. If you still want to sell it after all this, I wouldn't blame you in the lease.