Assuming your motors not a $2 hooker, it could be a thinner oil was used. If a guy from SAU did it though, there'd be no excuse for the wrong grade oil.
Sure its not just the injectors?; has it been thee always, but you've only just noticed it now?
RB injectors are noisy. If the tapping raises in Hz when you race the engine, and becomes quiet when on RPM decel, its the injectors.
That said, RB oil senders, gauges are notoriously shite for playing up.
IMO id put a known good, mech gauge on it asap.