The sound and picture synchronization are adjustable in the system menu. Refer to your owner manual. If unavailable you can find the manual at Bose.com.
Sorry can't be more specific at the moment, don't have manual handy.
This depends on the source. If this happens internally (from a DVD in the 321) then the problem should be able to be resolved by just resetting the 321. (unplug the power cord from the sub for 30+ seconds)
-If this is from external sources like a cable box, believe it or not, you can reset the cable box the exact same way. If resets don't fix this (and this is external) then check the cable box's settings for a/v delay compensation.
After sitting off for a few days the sound does not work until the unit is unplugged for a minute...
(More)
After sitting off for a few days the sound does not work until the unit is unplugged for a minute then plugged back in.