Try to localize the source of the noise. I believe you said you have a gas strut so it won't be the cocking arm dragging across the spring. Does your grinding happen during the whole cocking stroke or just part of it? Try lubricating the cocking slot with Krytox or moly lube. It is possible the piston skirt is digging into the side of the compression tube opposite the cocking lever, too. If this is the case buttoning the piston or rounding any sharp edges on the skirt may be your solution. It's hard to troubleshoot a problem when the gun is 3000 miles away.
Your pivot screw may be too tight or you may have some manufacturing leftovers in the pivot. If you feel capable (some are not) remove the stock - usually three screws. Remove the pivot screw. Remove the barrel. There should be no reason to go further. Use care to not the location of parts as you disassemble the unit and their sequence. Clean the area on each side of the barrel block and inside the forks. Lubricate sides of the barrel block lightly. I'd use Krytox here but if you're not into Krytox you may wish to try a lithium grease - it's not black like moly. Reassemble the gun. Tighten the pivot screw to the point at which when cocked, with the butt of the gun on the floor and the stock between your thighs, you can't move the barrel from side to side. If this appears to be beyond you either return the gun on warranty or check in with OleTomCat in South Carolina. He's the Gamo guru. Good luck!!
Silicone is a very poor lubricant for metal to metal. I would consider any oil viscosity inadequate. You should be able to procure a small tube of some kind of grease. Be advised that lubricant at the pivot point may ooze out a bit which is why I'm not fond of moly lube for that location as the black creeps. If you have plastic or nylon pivot washers the silicone lube would work. Silicone grease would be preferable to silicone oil. If you have fashioned brass or bronze pivot washers do not use silicone.