Q: Knocking noise from under the hood

Hi, thanks for writing in. There are many possible sources of the knocking noise you hear, especially with the advanced mileage on your vehicle. Most likely are worn connecting rod and crankshaft main bearings (will knock worse if you rev the engine in neutral), piston slap due to worn pistons and cylinders, even noisy valves lifters and timing gears.

With your mileage, there could easily be some crankcase "fumes" which can be very much like smoke coming out of the dipstick. As long as your crankcase ventilation system is properly maintained, the engine will burn these fumes - up to the point where you have blue smoke exiting your tailpipe.

I would recommend having a noise inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose this problem, get an accurate assessment of damage and cost estimate for repairs.