Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Loud hum in 3rd and 5th (2002 Nissan Frontier)

I have a 2002 Nissan Frontier XE (4-cyl, RWD). So I moved from MO to NC a couple months ago, and hauled a 6’x12’ U-Haul trailer over the Appalachians (I suspect this was the catalyst for the problem, but I could be wrong).

Now in both 3rd and 5th gear, when accelerating, there is a noticeably loud hum from (seemingly) the engine. I don’t really notice it in the other gears.

Any ideas? Thanks!

If the noise nearly disappears in fourth but is very loud in neutral with the clutch up the main shaft idler is the likely cause. If so it will soon be jumping out of 3rd and 4th. If so be looking for a good used unit. And yes, the trailer could have been the cause.

Hi Rod, thanks for your reply. It doesn’t do it when in neutral. Only when I’m in 3rd and 5th and pressing the gas (i.e., letting off the gas eliminates the loud hum).

Would this still be the shaft idler?

It may be. It’s just a text book diagnosis when all the factors fall in place. You might try coasting down a steep hill in third with your foot off the gas so the engine is slowing your speed. If it jumps out of gear my first guess is likely correct. But of course, you have checked the level of oil in your transmission… I am not a great fan of additives but the lucas engine oil stabilizer can help quieten manual transmissions and get a few thousand more miles out of them if added at the first indications of wear. It just takes a few ounces. If the transmission is somewhat low get the correct type lubricant and if you feel lucky add a few ounces of Lucas and then top it off with the proper oil. And if it jumps out on the down hill test a transmission transplant is in your future, regardless or the Lucas.