Altima 2002 5 speed 3.2-Have experience loud roaring noise (not from engine) almost like the sound of a hole in the muffler. Noise increases on acceleration with loss of power going up hills. Downshifting in lower gear causes the noise to increase and does not help the acceleration. At the end of a recent long trip, the temperature gauge went over to hot when I accelerated up a very steep hill on a interstate highway. I switched off the air and turned on the heat and temp went down. This the only time I had the temp go up. The car had a recent tune up and oil change. Mechanic feels it is air the I am hearing but can not locate problem . Any suggestions?