Need help with my Honda Higness

I've ridden my bike for approximately 5,000 km, and my third service is due on February 25. Recently, I had my chain lubed and tightened at a local garage. However, for the past 100 km, I've been experiencing a lot of vibrations on both footpegs, especially at lower speeds. It doesn't feel like typical single-cylinder vibrations; it feels more like my drive chain is running on sand, as if something is being crushed inside. Has anyone else faced a similar issue? Any suggestions on what might be causing this?