Help required! Hero Honda Splendor+ engine noise

I own Nov.'06 Hero Honda Splendor+ run around 8300 km.

From the day one, the engine makes a typical noise: same as of a Vaccuum Cleaner / Mixer Grinder motor (when the accelerator is lowered in high speed when the vehicle is running in any gear - as if a lot of air is sucked in through a small hole).

Can you please help me:

1) is this a major problem? & the origin of the problem.
2) How to repair the fault?
3) Impact on the engine (till date as well as if I don;t fix the proble - in future)