New brake rotor, but not new pads?

ok, so a few weeks ago I had a flat on my pick up, driver front, I changed to the spare wheel and tire, but it was so rusted, that it would not take highway speeds, and actually wobbled off on the interstate, fun right, NOT, anyways, it completely destroyed the brake rotor. This weekend, I finally had the money to buy the parts to fix the truck, I only bought a new rotor though, I cleaned and repacked the bearings, and ajusted them accordingly the rotor I bought already had the racers in it, I had the good tire put on the good rim, and bought new lug nuts for it, it seems to be fine, but there is a kind of squealing noise, very faint but its there. I think its just do to the fact that I have old pads on a new rotor, I know I should have replaced them as well, but I just didnt have the money, I will do it eventually, before things get bad. My question is, do you think that its just the old pads on the new rotor, or could I have another problem, I'm very paranoid when it comes to strange noises from my truck so please help me out if you can! I also made sure to repack the bearings with fresh grease, so I know thats not the problem