Between a new baby and house over the last year, my poor 07 700 has sat in the shop for about 6 months. When I parked the machine it ran totally fine and now it makes a loud metal tapping noise that gets quicker as RPM’s increase and match RPM’s when they decrease. I have tried letting it run for 10 minutes both idling and reving the piss out of it with no change. I have started it 5-6 times over the last couple weeks and two of those times the machine would try to turn over, but it stops as if there is too much pressure for the machine to continue turning over. Release starter button and push it again and it’ll crank and fire like normal.

Battery is new this year and on a tender. It does not make the clicking noise or throw any codes when it fails to crank/turn over.

No smoke out exhaust, except when it’s nearing redline when I mash the throttle which I think is normal for sitting for so long.

Sounds to me like it’s coming from the bottom end so I removed the clutch cover and it’s definitely not clutch noise. Something in the motor.

Could it just be bad gas?
Oil level is fine, but could it degrade and cause the noise?
Guy at work says maybe a stuck valve/lifter from sitting?
Mice chew a wire somewhere?