Sounds crazy, but I have heard of Bounder owner's complaining of the whistle sound coming from the round tubes on the grill. If your Bounder has the round tubes at grill, others have suggested removing the end caps and place sand in them to deaden the sound.
Will & Michelle
2008 Fleetwood Bounder 38P
2005 Jeep Wrangler Unlimited
1990 Jeep Wrangler