Burning Smell and Slight Knock
2000 Chrysler LHS, 75,000 miles (120,000 km).
Got the car at 60K, no oil was leaking, drove nice. I was using Castrol Titanium, which I have always used and is recommended by Volvo for my XC60. Made a change to Mobil1 because it was on sale and it seems like oil started seaping from everywhere. I have a burning smell from it.
My mechanic changed the camshaft thrust plate seals as they were for sure leaking. After that I could still smell burning and my mechanic changed the valve cover gaskets which appeared to be leaking too. Since getting it back I still smell burning oil, brought it back, they cleaned everything up and said it seems to be coming from the head gasket, which is concerning to say the least. Of greater concern, ever since the valve cover gasket change, when the car is warmed up, I noticed a knock with the hood open, it is hollow sounding and low frequency. It isn't very loud to be honest, but worrisome.
For the leak, I had a look underneath, I see some oil around a bolt connecting a black piece from the starter to the block, I see oil stains around where the diff. Meets the transmission and the stabilizer bar seems to have oil stains along it. It is really hard to localize anything specific. I have never heard of external oil leaks from the head gasket, so I am at a loss.
For the knock, it is not loud at all and the car makes decent power. I have noticed a slight miss/stumble since the valve cover gaskets were done, but just barely. Does this sound like a bearing issue? Could the mechanic have done something that is causing this could it be spark plugs or ignition related?