Bear with us, as it may take a bit of "back and forth" before some clarity emerges here...

The first thing I'd like to find out is whether the "clicking" is actually present at the back panel analog signal outputs of the receivers in question.

I'd check for this by listening to them again using their XL male outputs connected to the mic input/s of another system, (preferably all analog, "on the bench" and at some distance from your LS9 installation) ...as opposed to the listening you've already done via alternative inputs of the LS9 that currently exhibits the fault.

Now, if the XD-V systems prove to be "clean" at their own outputs, (as I strongly suspect they will) the fickle finger of fateful faultiness will be pointed towards the Yama-hoo-hah LS9, the first point I'd investigate being its set-up for "clock" reference.

I have had such systems default to their internal clocks, seemingly without human intervention, as a consequence of a power interruption during "down time".

It seemed as though all was well on arrival, so normal operations resumed, but "re-clocking" clicks eventually revealed themselves, forcing exactly the sort of investigation I'm suggesting.

Once paranormal activity had been ruled out, re-setting to the correct clock source cured the problem.

You will appreciate that it's the analog inputs requiring the most amplification (the lowest level ones, ...those at mic level) which will suffer the most, followed by the "quieter" of the line level sources.

Digital inputs, however, may simply (and silently) perform a "phantom" re-clock "in sympathy" with the LS9.

In any case, there's nothing subtle about an external data stream or expansion slot system trying to operate in the absence of a correct reference, as the regular, rhythmic "splatting" that ensues is almost at full level.

Given that your XD-V receivers are "clean" away from the LS9, but you find that "phantom reclocking" is not to blame, I've also found that the Yamaha's TFT colour display screen and the console itself can radiate quite an array of rhythmic RF "junk", so a physical repositioning of your gear may be the answer.