Hi everyone. I have a 2003 BA with 145000 ks. There is a knock in the engine on a cold start up which goes after a few seconds. It can be quite loud sometimes and sometimes it's not there at all. My local mechanic thinks it may be an oil drain back issue where there is no oil in the top until pressure builds up. Are these engines fitted with a oil valve that may be faulty and allowing oil to completely drain from the top end. Thanks for any help.