Help Please

[Bart Lyons <blyons@belfast.oilfield.slb.com>]

Good morning, I recently purchased a used Gibson Echoplex
Pro Plus and Gibson Echoplex Pro (the older unit upgraded to Loop 4 198
second). The reason for two was I wanted to run a stereo rig. The pro
plus came first and it sounded great connected through the AUX on my
Mackie Mixer. The second, purchased from Bristish Audio in the US arrived
a few days ago. So following the manual I proceeded to set-up the two
units to operate in stereo mode. Everything good so far the two units are
in perfect sync via the brother and midi connections. But disaster
strikes there is really bad digital type crackling noise on loop
playback. I've checked all the input levels, used the shortest leads even
tried changing which unit acts as the master/slave. I can isolate that it
to the older unit but it works perfectly on it's own i.e. not in stereo
mode. I've checked the Loopers Delight Q&A and cannot find any
reference to something like this can you please help as I don't know what
to do.

Thanks & regards - BART