It would seem to me that the "crackle/bark" you're getting isn't any indication of detonation- at idle/unloaded you won't get detonation (unless the ignition timing was WAY too far advanced) anyway.
Is there a way to reduce the header/sidepipe noise volume to a lower level? Like w/temporary baffles or an additional muffler system to use long enough to see what (if anything) you can hear?
Another idea would be to do some acceleration testing to see if there was a reduction in speed w/the timing you'd like to run (w/the gas you are going to use). If there was no slowing from the timing you "like", then that's a good indication there's no detonation- detonation kills the power, so you'd expect to see a reduced speed/increased ET if it was detonating.