Advice needed on a FX loop switching project

[chimpzilla]

I'm looking for some advice on a switching unit I've been asked to build, and need to see if anyone can see any problems with ground loops or switching pedals in amp FX loops

I've a guitarist friend who runs a 2 amp setup and he's asked be to build him a unit to do some switching.
- Firstly he wants an A/B switch between the two amp inputs (not A/B/Y) so this I can do.
- Secondly he then wants his effects to be switched between the two amps FX loops. I'm pretty sure I know how to do this, I just use an additional pole from the switch to drive  a bank of DPDT relays. So if AMP B is selected I use relays to isolate the ground and the signal at AMP A FX send and return (so that's 4 relays or 2 DPDT relays to isolate amp A). Then use the same configuration to isolate loop B when amp A is selected

My main concern if when I re-engage amp A will there then be an loud popping or banging as I'm switching the ground in / out on these FX loops ? 

For the switch I'm planning to use a 4PDT so I can do the A/B, change a bi-colour LED and switch the relays.