[DK on the road]

 Can you hear loose valve lash in a diesel like you can in a gas engine?

Typically, valve lash is not loose, but too tight. 

As the valve is closed by spring pressure, with 500 down to 200 lbs of progressive spring pressure at 750 (1,500 rpm) times per minute and 1,200 deg temp of exhaust temperature, the valve head gets mushroomed out and the valve stem gets stretched by .002-.004 or more after 2,000 hrs or 80K miles. 

Once the valve is stretched too far, multiple bad things can follow. one example...

The valve can be held open as it rides on the small side of the cam. Also, as its getting close to no lash, the valve and valve seat begin to burn get hotter and weakened further. Depending on the particular motor, the valve touches the piston, and the valve breaks off, and pulverizes the piston and puts a hole in it and/or grabs the sleeve. At times, I've had the piston get wedged, breaking the connecting rod at the wrist pin and spinning the loose balance of a connecting rod around the crankcase for 2-3K times, cutting the cam and block in 1/2.   OHHH the pain, disappointment and expense.

I could go on from all motors I've blown up racing.

IMHO, A maintenance routine is way cheaper than the alternative.