Mark X wrote:
Lawn mower makes an intermittent very loud screatching noise when in
use. The start pull cord loosens slightly when this happens and there
is some vibration from around the pull cord casing.

The mower is a Briggs and Stratton Sprint 375.

Any ideas?

Very common - The pull start clutch shaft needs lubrication.
Take the pull start cover off.
Pry the metal cap off the clutch - now remove the ball bearings.
Now remove the square drive - lubricate the shaft with a small amount of
grease. Not too much or it will run down onto the balls and they won't work
as a clutch.
Reassemble and make sure the square drive only turns in one direction.
They can size to the shaft and alas it is part of the crankshaft, in which
case I would take it to the dealer. BTW I've fixed lots of sized ones - you
don't really need a new crank shaft!

Slatts