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I'd 1st suggest measuring the actual oil pressure with seperate mechanical gauge - this can be plumbed into the engine via the current pressure switch port -
If you do have a low pressure reading then replace the oil pump and ensure that the pump pickup in the sump hasn't come loose or is blocked
my thoughts are that the rumble is a worn main bearing and the tapping noise is a valve / cam follower
both of these need a full level of oil pressure to function