Peng, you were one of the people who originally tried to help me with this issue, and I am definitely no expert, but I went through three AV7005 Marantz units, and I had problems with all three. I purchased the first two from Amazon and the last from my Home Audio Guy. I spent about two weeks, trying to ground, checking to see if the was the cable box, all the trouble shooting that was suggested when I posted this issue about a year ago in this forum. Nothing worked.
I do remember another member had some humming issue but I don't recall anything about crackling. Again, considering that Marantz has sold a lot of units, it is not nice but also not so surprising that a few went defective. I just plowed through the AVSforum owners thread and they happy, one reported no issues with his Emo amp.
At the time I was upgrading from AVM 30 Anthem Amp and when I hooked it back up, no buzzing etc.
That is really puzzling. Preamps and amps are such a mature technology, there really isn't anything about "compatibility". My AV7005 is working perfectly with an Anthem MCA20 driving my L/R, a Adcom 555 (using one channel) for the center speaker, and a Marantz MM8003 for the surround channels. It is also connected to one of my separate system (Cambridage Audio/Bryston) via zone 2 so that's a lot of amps it has to be "compatible" with, yet I have experienced no hum, hiss or any noise issues.
also tried different interconnects, which are not cheap

. When I demo'd the Intergra 80.x and when I purchased the AVM50V I did not experience this issue.
I really don't know what to say. If you had tried 3 units, I would agree it was unlikely all 3 units would be defective, but I strongly believe there was a culprit that somehow was able to escape you.
If you even check some of the reviews on Amazon about the newer 7701 people are having the same issue. One person even pointed out Marantz Technical support stating that some amps are not as compatable with their equipment. (I do take that with a grain of salt) Either way, I am not saying your wrong, but I think it you are going to spend that amount of money for a P5, It might be a smart idea to test it out first.
I will check it out, I just thought I should check AVS first for the obvious reason. I am being tempted to upgrade to the AV8801 so I will check out some 8801 user threads too.