funny sound top end

[wreck-n-roll rik]

I am the new owner of a 1998 KX500, and new/old to dirt bikes in general so I need some help.  I'm not familar with this motor yet.  It is making a top end low-tone rattle.  The prevous owner did not have a crush gasket in the head to pipe, and only one o-ring.  I like to go through new toys whe they are used, so I put in the gasket/o-ring/new springs... This is when the noise started, so I took the gasket out but it still makes the sound.  Any Ideas on what it could be?  I also cleaned the carb and replaced the plug and put in freash gas (91 oct.).   

[kiwimonster]

i had a noise like this it was my exhuast springs touching the pipe as vibrating, i put somw heat proof hose over mine and it went away.

[hughes]

If the KIPS valves are worn some they can make a light rattle noise. High temp silcone works great on those pipe o-rings and adds some dampering.

[wreck-n-roll rik]

Thanks for the suggestions - I'm going to get a manual and this week-end and really get into this thing.  Not a lot of time to left ride here in Northen Minnesota so this winter the Bike will go through some major rebuilbing...  Sure is a powerful bike, scared the cr@p out of me when I test a test ride.

[Johnniespeed]

On my 04 kx500 the funny noise was caused by the upper pipe mount. This is on the right side of the bike . The frame broke out and at certain RPM the broken mount would vibrate against the frame. When I first heard it I thought the KIPS was rattling. I now have learned whenever I hear a noise like this, it is related to pipe mounting.
  I also had issues with springs falling off, when using the stock pipe. With the stock pipe I used shorter springs from an orange bike. With the FMF pipe, the stock springs seem to stay on.
  John