Is this lifter noise? 95 NAS V8 D90
I hear a "machine gun" tapping noise coming from the driver side of the engine compartment in the last few days whenever I press on the gas semi aggressively, especially in 1st gear. The noise becomes very subtle as I shift to 3rd or 4th but I think I can still hear it. If I downshift, though the revs increase, the noise doesn't occur.
It doesn't come on for the first few mintutes with a cold engine but rather when the engine warms up. I've had the car less than 1000 miles (26,000 miles on new engine block) and the PO always used either Mobil 1 0W40 or 10W40 Synthetic High Mileage. If it is lifter noise, would adding something like STP ZDDP treatment help? Just don't want any wear/tear after all of the prior owners took such great care.