Bottom end growl/rattle

Got my 1.6 gti up and running after restoration and it's developed a growl/rattle in the bottom end which sounds like it's from the gearbox side of the engine.
When ticking over you can't hear it but the more and more revs the louder you can hear it.
Dropped the oil out which is new and there was no metal filings to be found, carried on to drop the sump which had some white residue and check the crank with no obvious movement.
Oil pick up had stuff on it but wasn't metal.
Took the closest crank cap and piston cover off and couldn't see any scoring either.

I'm a bit unsure where to go from here to be honest if anyone has had similar issues I'd love to hear them.
Also are these bolts on the crank covers stretch bolts and need renewing? Cheers Jason