The fan isnt driven off the water pump. Its attached to the 'fan bracket' and thats most likely what is causing the noise. Isuzu lists 2 different ones depending on the month it was made.

BRACKET; FAN 8-97148-675-1 08-1997 to 07-1999
BRACKET; FAN 8-97231-718-0 08-1999 and LATER

If you go to myisuzuparts.com and do a search for one of those part numbers you can see an exploded diagram of what it looks like.

--Dave

1999 Rodeo LS 3.2 4x4 5 Speed
32x11.50-15 BFG T/A KO on US Wheel 94 series
3" Lift - Rancho 9000x
Rear No-Slip Locker
Flowmaster 50 series SUV 2.25"

There is a very fine line between "hobby" and "mental illness." - Dave Barry