Engine Cooling System problems of the 2008 Nissan Titan

I bought a brand new 2008 Nissan Titan crew cab truck back in Sep 2007 no later then 3 months later it started to make a funny noise that I was uncertain of so I called the dealer ship immediately and made an appointment to get it looked at the first time was back in Dec 06,2007 left the truck in the dealers ships hands they had my vehicle for 2 days when I came back to pick up my truck Dec 08,2007 they had explained to me that they could not find the problem they explained to me that they did the 7,500 maintenance and also changed out my timing belts maybe that would be the issue so I took the truck home the next day the noise was still there so then I made another appointment the available appointment they had and was offered to me was April 11,2008 now this is when the 3,000 maintenance was due for a check up so I left my truck there again by the end of that day they called me up and said my truck was ready to be picked up so I went back that very day picked up my truck same thing maam we cant find the problem so now im irritating so I asked to speak to the service manager explained my situation and then again they made me another appointment to come back check my truck again so I made another appointment to get it looked at again. I brought my truck back in again to get it serviced may 02,2008 this time they changed out the coolant the oil the timing belt again so I picked my truck and still the next day its making noise but a little louder so then this all occurred within a couple of months apart not to mention I have all the receipts to prove my issue and I went again this past month oct 21,2008 to get it looked at again still yet cant find the issue they had explained to me that they changed out my air condition filter then they changed out the timing belt and not to mention they explained to me that they order another part to fix the problem that will make the noise stop but mind you this is the 4th time.