Hi, I have a REL Strata 5 which has been great, but now I have an issue. Searching the forums I've found posts on humming and ground loops etc but I'm not sure they cover my exact problem. When the sub is on I generally get a pulsing hum sound from it, at approximately 1 hum per second. If I change the phase to 180 from 0 it will change to a strange strangled constant hum. Here's a list of stuff I've found/tried so far: Disconnecting the LFE cable form the sub - no change. Disconnecting the High Level input - no change. So at this point I've got a stand alone sub with a humming issue! Rebooting the sub - hum will go away for a while and then randomly come back on. Changing LFE and HL levels/cross-overs etc has very little effect on the problem. Turning off my Amp (STR-DA5200ES) and the hum stops - even though the amp and the sub aren't directly connected anymore. Connecting Amp to same electrical socket as sub - still hums. Putting a mains rectifier (cheap maplins job though) on the mains socket - still hums. Putting the Amp on a completely different mains socket - still hums. Connecting the ground of the Neutrik (or whatever it's called) connector to the ground on the amp instead of the negative speaker connection - still hums. The sub appears to work perfectly well other than the hum - bass reproduction in movies etc is fine. The problem has been suspiciously coincident with the purchase of the amp. So looking for any good suggestions on how to fix it, or in the worst case what a good replacement sub is that should be of at least the same quality. Cheers in advance.