I have a 2005 f150 4X4 fx4 when going apx.30 mph sometimes it seems like it is trying to kick in 4wd and makes loud noises. Switch is in 2wd high, has done this 4 or 5 times in last few days and also seems to slow truck down like the brakes are on .I have checked all pads and are all worn even.The truck has apx.30k miles and is still under warranty just wondered if anyone else ever had this problem???

 

Check the vacuum lines and hoses running from the solenoid to the hubs. If there is a vacuum leak it can cause the front hub to engauge and make a grinding noise.