Have you throughly cleaned it... I mean REALLY cleaned it.
Many 17 HMR shooters treat them like 22 rimfires, and the cleaning is almost non-existant.
But these little puppies do copper foul, and it doesn't come out with a lick and a promise.
Use wet patches with copper solvent - don't use brushes.
Keep wet patching, with 30 minutes between them to soak, until the patches come out white.
I doubt that Marlin will re-barrel it, the cost would be as much as a new rifle.
Also... do the regular checks - make sure the scope is tight, stock screws are tight, etc...
Here, kitty kitty kitty.
LRH member #23