tapping/knocking noise on 2000 vauxhall astra

[vauxast]

sometimes have a knocking noise on my astra it sounds like it is from top of engine it does not do it all the time some one said possibly knock valve? it is a 1.4 16v any one had the same or any ideas thanks

[rdv]

does it only occur under load, if so it could be detonation and after a few 'knocks' the knock sensor should tell the ECU to adjust things accordingly. a higher octane fuel like Optimax should prevent this . it could also be a faulty hydraulic tappet but this is more of a ticking than a knocking

[geggsy]

first of all chek your oil level. then inspect valve clearances. do the obvious checks first. have you had it serviced recently? if spark plugs have been changed have they been tightened??