Buy a cheap GPS Speedo that sits on top of the dash and does a heads up display on the windscreen

Auxiliary belts slipping. Need tightening or replacing

From that position a gentle rotation of the engine using the pulley bolt will guide it on

Jack one wheel off the ground, place it in a high gear such as 4th (if it’s a manual) and turn the wheel in a forward direction and the engine will turn. Taking spark plugs out will also make it easier to turn.

Sticking caliper or failing flexible hose. Hopefully just needs a clean up and rebuild.

The source is the pads vibrating in the caliper at light pedal pressure causing dry metal against dry metal. They need removing, cleaning and re-installing with a light smear of high temperature grease at the contact points between the pads and caliper.

Always been a thing that you shouldn’t run a tank that low as it can then pick up ‘crap’ from the bottom of the tank but no idea how true this is. There should be a filter before your high pressure pump anyway which should catch any ‘crap’