Alesis Andromeda A6

yes you can test it , just upload it to any patch desired in the
userbank. if possible download it it makes the following test easier (
see manual under sysex, switched b.e. to download "here")
Another Idea:
take the defaultpatch you mentioned. ( make sure the modulationwheel
is completely down and to be even more sure turn down all the lfo's in
speed . ( just in case these caused it) . 
now if you still hear it : does it change when you turn the fine tune
knob of oscillator two ( the one on the right under the big one) ?
if Yes try this : put voice assign to rotate ( to pick a new voice
every time you press a key ). watch the voices used under 
global->voxmonitor: do different voices have a different "beat"?
it's normal they all sound a bit different although a beat faster then
lets say once every 4 to 5 seconds to my opinion is too much. 
i had a similar problem which in my case was restricted to only some
voices and even to only certain parts of the keyboard. after
establising the problem properly i took advantage of the guarantee and
2out of 8 of the oscillatorchips where swapped.