Not saying it isn't, just that it could be caused by the loss of damping and isn't much to worry about. If it gets worse then it'll be easier to find the culprit, in the meantime - it's not doing any harm, is it?
If you can't settle for that, replace the other tensioner and grease your pulley shafts (giggidy) and see what happens.
If you can't settle for that, replace the other tensioner and grease your pulley shafts (giggidy) and see what happens.