Tapping sound from air filter

Open it back up and let the squirrel OUT!

 

I'm suspecting a camshaft lobe failure is coming.
Standing beside the engine with the hood open,Check when you turn off the engine if the tapping sound follow the engine rpm decreasing ?
Ben

 

Truck sending you morse code:
Get Steering Shaft Fixed.

 

If your tapping noise is involving injection system of your engine the noise will be eliminate when you turn the engine Off from idle.
I'm guessing the noise will follow the engine Rpm. . .(camshaft lobe)
Let me know the result please.
Ben

 

There is another possibility if your tapping noise is there only under engine load i remember many years ago there was a Volvo bulletin to add a special baffle inside the turbo on the intake side close to the turbo compressor wheel, that special baffle is hold in place by a big snap ring.
The purpose of the baffle is to eliminate the turbo pulses (can generate drumming in the air filter housing)
Did you replace the turbo recently ?
Ben