tyre noise and correct tyre pressure for high temp

I have 2008 Dodge Durango milaege is about 127000km , with standard tyres, I use it mainly on regualr tarred roads, for school run etc, though occasionaly go offroading in the desert,  the avearge temp  here are about 45 degrees celsius in summer can get to 50+  so Im not sure of what tyre pressures they should be at, currently at 33psi as per label in drivers door I would like to know what could be causing the annoying noise when I'm driving most notable between 80km to 110km per hour. its like hum/whine  and its not my bearings have had them checked and not my kids in the back either