Humming Sound while driving that goes away while turning left

ScooterMD · 2018-10-13T14:44:13+00:00

2007 4Runner Sport here that has developed a medium-pitched humming sound while driving at all speeds. The sound has gotten slightly louder over the past year. I noticed just recently that the sound goes away when I am turning to the left or even just on a straight road that veers slightly to the left. It returns immediately after straightening the wheel. The truck otherwise runs well. I have two sets of wheels/tires - highway and off-road, and the sound is the same with both sets. I have had 1.25" spacers since before the sound started. The alignment seems fine. However, I had the alignment done at the dealer about a year and a half ago, and they had a really difficult time aligning it properly. I don't recall the issue, but I remember they had to adjust settings to the max to get it right. Any thought on what this could be? I am stumped.