Try the 300/4L IS sometime - an even louder clunk you can hear and feel, and during operation the IS is sort of a low growl.You're not wrong about the rowdy IS in the 300 f/4is! That's a perfect description of the sound. You can hear it from half a block away! But a small price to pay for a wonderful lens. I should never have sold mine when I upgraded to the much quieter 300 f/2.8is.
The 300 f/4is must have been one on Canon's earliest IS efforts. It must have been mid 1990's when I got mine. And apart from getting quieter, hasn't IS matured in the meantime?