Losing oil pressure?

You can verify the low pressure with a mechanical oil pressure gauge, but since you're hearing the lifters suspect excessive engine bearing wear, low oil level, or the oil is too thin from being diluted with raw fuel. If the oil seems to run off the dipstick like water, change it first to see if that helps. Raw fuel in the oil can occur from a recent no-start condition where the injectors were firing but there was no spark. Coolant in the oil from a leaking head gasket will melt the first layer of metal on the crankshaft and connecting rod bearings.