Marantz AV7701 buzzing .

Hello,
In 2012 I purchased AVM 3.2 pre from USA tube
It has HT bypass.
I was using it on Anthem Pre receiver before as prepro-no issues btw..
I then bought marantz pre pro-AV7701
since then have had issues..
when i connect RCA cables to Ht bypass connection on pre to line out for F and R channels I simply get a buzz..no sound..when i turn on pre with connections made I get a speaker pop.. .. the surround speakers and front channel speakers are connected from pre to Marantz pre using balanced cables
The front channels are connected to AVM and then then to Bryston amp with balanced cables.
when i have surround on get buzz in surround and center channel..these are what connected to marantz pre..
NO sound or buzz from the fronts. ie bypass not working..
when i turn off AVM or disconnect the bypass connection between the AVM and marantz pre out buzz stops.. but of course no more surround.
It sounds like maybe a ground loop issue (buzz is steady not really increase as buzz does not really increase all that much) but even with buzz getting sound out of ctr and surrounds ,, nothing from fronts..
BTW when I connected the xlr cables for the front from the AVM to the fronts of 7701 to marantz MM7055 amp which I use for surrounds and center and sub only(thus the bypass because prefer AVM pre for music only) No buzz.
A real pain have to switch front xlrs and speaker wires from AVM/Bryston respectively to Marantz pre when want to watch movie. .. which is what of course o I have HTB..
any input would be GREATLY appreciated

EQUIPMENT
Bryston 4bsst2(for 2 channel listening)
AVM PA 3.2(used for 2 channel music and HT bypass -love AVM pre for listening.)
Marantz AV7701 Pre-used for surround
Marantz MM7055 5 channel amp used for surrounds center
Signal Cables XLR except on the HT bypass when have to use balanced cable from AV7701 F &L pre-out to AVM bypass connection
Simaudio 3.2 Cd -with balanced connections
Klipsh RF7II with surrounds