Sounds like Hydra is dead on. Mine does the same. Loud as hell, sounds like you should be breaking the sound barrier. Then it goes away and all is well. Not any loss of power, just a lot of irritating noise. Will do the same thing when the engine gets real hot, like idling in hot traffic.

 

Actually, mine still works. I'll keep off the mod until I really need it.

 

I've been wanting to check into that with the 19.25 flex fan pulled back far enough and leave enough room for a puller electric fan because the 5.2 and 5.9L 1998-1999 didn't come with one so they like to get hot in idle and the A/C don't like to work.