Hydraulic valve lifter- noisy tappets

I have noisy tappets… The time taken for them to go away is getting longer and longer, and is around 5min now…

I used Wynns Hydraulic valve lifter when i last changed the oil (bout 1000miles ago)… Shall i put another tin in??

Went to motor-world to buy wynns, and they tried to sell me slick50 (3 times the price), but told me it works… Please advise..!!

How about chucking a litre of ATF (Auto Trans Fluid) into the oil, running the car gently for around 15 mins, then doing another oil change?