CG Whining

Quick question on the CG repair I'm doing.

Have finally got the rear wheel sorted (spindle was rusted in, rear brake rusted in+seized, took almost 2 hours of swearing and then an hour of cleaning, polishing and greasing), so the bike's now rideable. When pulling away the bike makes a whining noise as the clutch engages, almost like it's struggling.

Is it likely to be because the oil's been in there for yonks, or could it be the clutch? Or is it just a normal noise that I just don't remember from riding it over a year ago?

The chain's probably on its way out, but has been cleaned+lubed and is at correct tension, and seems to move easily enough when off the bike.

If it's been stood for ages I would have been tempted to change the oil before running it.
Could be alsorts I suppose. It would be worth changing that oil and seeing if it goes away.