I've found that the amount of extraneous noise my engine makes is dependent on how hot the engine gets. The other day I was out riding in 105-degree temps, moving relatively slowly on occassion to the point my temp gauge was hanging at the midway point and the fan kept kicking on. I noticed a lot more whirring, ticking, clattering sounds coming from the engine under these hotter conditions.
I use 15W-40 Rotella. 40W oil tops out at 104 degrees on the owner's manual chart for recommended oil weights/temperatures, if that really means anything. If it was this hot here all the time, I'd probably go with a 20W/50 oil in the Summer as recommended by that chart.
Under 4K RPM restrictions really suck, don't they?