There are three bolts holding the upper shroud/fan cage to the lower shroud @ the 9,12 and 3 O'clock position. These can back out on you and the shroud will make contact when the fan clutch is engaged - say, in the morning when it's cold or under load (engine heats up). If it hits bad enough your fan could come apart on you, which can get expensive quick.
Passenger side bolt is a bit of work to get to, need to remove air cleaner, some brackets and the cold side intercooler pipe. Make sure you use locktite when you tighten them up of the same thing will happen again.
FYI, my top and passenger bolts loosened up on two separate occasions.
Definitely sounds like it could be the bolts. Your saying you were pulling with the engine cold though? My fan usually engages for a minute or two when I first start it up cold, I would warm it up before pulling though. JMO
A thermal fan clutch is engaged on a cold startup because the fluid drains into the working area when the engine is shut off. The fan clutch will slow down shortly after startup as a result of a pumping action produced by a difference in speed between the shaft and the body of the clutch.
i wasnt pulling when cold, it was warmed up, i just notice the noise when cold every morning and when you get on it, and just then when pulling the sled it went a little crazy louder than normal. after my dinner i will check out the fan shroud bolts thank you guys