If its vertical-i.e., you feel a slight tick when you lift the saddle up, it's more likely will be the DU bushing on the shock eyelet itself. This is a low friction bushing that the pressed in shock reducers(the aluminum collar/spacers) slide/rotate against as a swingarm goes though its movement. These will wear out in time and can be replaced by the shock maker or a GOOD shop(ask them if they can perform the service-if they understand what you're saying you're safe). The bushings are pretty thin so if you try to push out the old one without a proper sized tool you can bung things up in a hurry
Usually bikes with bearing rear assemblies stay pretty tight. If you want to trouble shoot you can remove the just the rear shock bolt(keep all linkages attached) and cycle the swingarm without it attached to the shock. If you feel slop after checking proper torque on the bolts then you could have a bearing issue.
