My sv650 2nd gen makes quite an odd rattling noise when I'm in the 4,000 RPM range. Higher than that, not so much. I'm a little concerned, and thought I'd drop the question of what might be causing it.
Does it rattle in neutral at that rpm or only while in gear riding? If it rattles in neutral, bring up to 4K and start grabbing parts and listening for where the rattle is coming from. Could simply be a loose bracket that is resonating at that rpm.