If they did adjust the valve lash they could have made it overly retarded or too advance this will make the engine run hot causing overheating to blow the headgasket. When you do a valve lash adjustment the ignition timing changes, therefore the ignition timing must be retime.
The noise you're hearing is probably detonation/spark knock which can be cause by an engine overheating.
Hope this helps-Good Luck.
Thursday, April 26th, 2007 AT 3:56 AM