Again, it depends on what is whistling.  The sound-play words are intensifiers, not valences.

• 01.092 like the whistle of an engine coming out of a tunnel.
• 02.002 Bilbo began to whistle loudly
• 05.112 a whistling
• 05.143 Whistles blew,
• 07.030 and when I call or whistle begin to come after me –
• 07.051 So Gandalf gave a long shrill whistle,
• 07.061 They don’t seem all to have come when I whistled.
• 07.062 Go on, whistle again!
• 07.063 Gandalf whistled again;
• 07.100 its whistling voices were released.
• 12.022 in fierce whistling steam,
• 14.040 Above the borders of the Forest there was whistling,
• 17.039 and arrows whistled;

“whistle, v.” OED Online. Oxford University Press, March 2015. Web. 29 May 2015.