Doesn't take 2 days for oil to drain back from the sender. Initially I would have suggested a possible intermittent sender however:
The fact you leave it running for "2 minutes with the light on" means you really have and continue to fuck up your engine (to be blunt..) - I only say this as the low pressure clearly coincides with the noise due to very poor oil pressure - sub 8psi iirc

I would still suggest getting a oil pressure gauge on there and see what its actually doing before going further.