I've seen it on belt drives but not idlers. The phenomenon was referred to as "breathing", possibly attributable to an imbalanced platter combined with unilateral pull from the belt.
All the best
All the best
garrard 301 and its' restorations
i was looking at a recent you tube video of a restored garrard 301 in action. the platter motions while playing an lp were very "wobbly" and bouncy ,like it was tracking a warped record or a spring in the suspension was "detuned" is this an optical illusion or is this normal to the idlers ?. i've never seen this on a vpi ,acoustic signature ,technics 1200 direct drive , kronos ultra high end etc .