My take on this would be........to take away some of your doubt and when you can given lockdown,......put a bottle of Wynns Lifter Treatment straight in your engine if the oil/filter is fairly recent and clean(ish). Give it a fairly long run to let the engine get to op. temp. and run for about 15 mins - start by letting the engine tick over at home with the odd rev til the fan kicks in, add the Wynns and then drive some distance preferably where you can keep the engine revs at 2.5/3.0 rpm - use 3rd gear if necessary - for 15/20 mins. Drain oil overnight or longer if you can to get as much old oil out. If your filter is recent, you could leave it as is - its not gonna harm too much and the small residual amount of Wynns is not gonna kill. VIP - use a 'premium' brand of 10/40 semi e.g. Shell or Mobil - no own brands stuff or cheaper less well known brands. After leaving the refilling as long as possible, put 5.4 ltrs back in if no oil filter change - 5.7 if you did. It could be that on your recent cam covers change/sealing sees that a bit of silicone sealant skipping around that could part block the lifter temporarily. See if that changes things and if not, its only cost you an oil change and the Wynns stuff as part of eliminating the cause. Check oil level next day. Drain down is always gonna happen at some point and experienced at various lengths of time since last shut down - that will depend on your mileage, previous care re oil quality changes and temps at start up. Main point despite all this,is that if it quietens after a short time it not a serious issue. Ant.