Piston slap will give you s strong tapping noise under load, especially in mid range to upper RPMS. You said it has been cold lately. Pistons can get quieter as the engine warms up and I am talking after about twenty minutes of driving.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!