Australian Car Repair Issues? Ask an Auto Mechanic for Answers ASAP
Your noise could be an idler pulley, there are three pulleys, two fixed, one tensioner.
Could also be power steering pump noisy.
Have you checked all the fluid levels recently?
Can I suggest you get a really long screwdriver, you can use it as a stethoscope to listen to all the rotating pulleys.
Alternator, waterpump, Power steering pump, and three idler bearings.
Once you have located the cause, you need a 15mm socket and bar, and you can release the belt tensioner to remove the belt.
Anything in the front of a VY or earlier is easy to fix.
Last of the Holden V8. Roller cam engine.
What did old oil look like at the change?
What oil have you put in there now?
How loud is this knock in the engine?
How long does it last after cold start?
Do you need any further help with your cars?
I hope my advice has been of assistance to you.