check the camcover , where the oil is put remove lid while engine running check its is not vaccumed when engine running or pull out dip stick and see if it pulled back in on its own sort it quick if it is new camcover needed makes a loud air escape noise or like a slipping belt sort of squeel noise causes oil loss as it sucks in crankseal to let engine oil fumes breeth dont buy a cheep one off ebay get a vauxhall one if needed cheap ones dont last a few tho miles knocking noise most likely anti roll bar link
soxthe cat
April 2012