Sounds like chain "free spinning"...? Please clarify, as the primary chain is normally tensioned to "grip" cogs without slipping, and may have a bit of a "whine" from the chain rubbing on the nylon tensioner. Was bike recently serviced?... i.e. did you change oil/lube or forget to fill the fluid up to the proper level? Do you have a service manual and access to simple tools to pull inspection cover to check it and if necessary adjust it properly?
Ohhh. This could be bad. Does it sound like the sound is coming from the right side front of the engine? The nose cone area? Or is it coming from the primary side? If the former, pull the nose cone and check the condition of the tensioner shoes - both the outside one and the inside one (use a cheap dental mirror to see this). If you have a bunch of tensioner shoe material inside the nose cone when you open it up, that is a dead give away. You have to clean out the oil system BEFORE running the engine any more. If this is the problem, consider up-grading to the roller chain configuration.