Another thing you might try would be to use a PocketWizard MultiMax in sniffer mode to determine where the interference is strongest. Unfortunately the new PlusIIIs don't have the noise-sniffing feature, so the expensive one is the only option.
If you are anywhere near LA or San Diego, I can loan you a MultiMax for the test.
If you are anywhere near LA or San Diego, I can loan you a MultiMax for the test.