My bike keeps making this grinding noise around the back wheel/casette/chainring area when I get speed on a tech/ jump trail

Question

It is an older bike that hasn't been used in years and I recently got it serviced and began using it on the trails. It is a specialized stumpjumper from around the 2004/2005 era and everything seems to be running smoothely except for the noise.

Answer 1

There are many...many potential root cause for the noise.

Firstly, you mentioned that you had it serviced. It could be good if you describe what kind of service it entails?
Many a times, shops claim full service but it's just a wipe down. (in my country)

If the service is complete, there shouldn't be any noise right?
Let's assume from here that the service is a wipe down.

Secondly, the drivetrain.
Was the cassette installed properly? - If not, the cogs may not be fully engaged in the freehub body and cause some slippage.
Was the chainring installed properly? - At speeds, a little anti-squat can cause your chainring to rattle.
Is the chain too long? - Exacerbates the anti-squat effect. + of course chain slap.
Is the derailleur properly indexed? - If not, at jumps, the chain might be forced to shift or rub against the next cogs excessively.

Thirdly, the wheels.
Is it only freewheeling that you hear the noise? Or does it happen at high speed pedalling too?
Is the tyre bead seated properly in the rim bed?
What's the lacing pattern on your wheels? - could it be that the spokes are rubbing under constant fluctuations in tension at speeds?

Lastly, the bottom bracket.
Is it installed incorrectly? - This is the least likely root cause, as it'll cause problems regardless of speeds.

Hope you understand that like doctors, just because it hurts, doesn't mean the doctors know what syndrome you have. I believe that more information is needed. :)

Also, I didn't even mention the rear shock (I'm guessing there's one). By itself, it requires so much TLC, and that's a whole new topic already.