[hec983]

I've been trying to diagnose this issue I've been having since the purchase of my 1999 4Runner 3.4l 2wd. When I'm cruising under 10 mph and on the gas, everything is cool, but when I left off the gas you wait one second and you can hear this humming sound. It sounds like its coming from the engine only when coasting under 10mph, slightest pressure on the gas and it goes away. You can hear it whenever you are coasting or coming to a stop, until you go over 10mph then it goes away. Any ideas??

[Semper_Fi]

my 98 does this as well so I am interested to see where this goes

[hec983]

Originally Posted by Semper_Fi

my 98 does this as well so I am interested to see where this goes

Really? I gonna check the power steering.

[Semper_Fi]

Originally Posted by hec983

Really? I gonna check the power steering.

just put a new one on mine if that will save you some time

[awthorn]

How slight are we talking in the sound? It could be happening all the time but then once you push on the gas the fan muffels it out. Have you checked your belts? Tire pressures? Tire grooves? Just my thoughts, good luck!

[Buckaroo]

Vacuum leak?

[Kanger328]

When I hear humming I think wheel bearings. But you say it's coming from the engine. Sure it's not the wheels area?

[wc11]

Mine did the same.
At 1st, I thought it didn't know the words.

In the end, right rear wheel bearing was on it's was out.

[hec983]

It doesn't do it all the time tho.

[Doc2012]

Possible it could be the joints on the DS going out.

When you give it gas, the load from the trans forces the shaft to spin, making the sound only come when it's got no load on it.

See if there's any play in the DS. Get under it and try to wiggle it. If it moves, its probably the joints, which can be replaced.

If not, then check the wheel bearings. Jack the truck up, and holding the tires at 6 & 12, shake them. If there's a lot of play in the tire, the bearings are bad.

[Acorn22]

Thread resurrection! I've looked everywhere and can't find a definite answer to this...

So I have a 98 limited and since I got it in December, I've had this weird whirring noise that only occurs when I take my foot off of the gas, sound goes away even with the slightest depression of the throttle. Since then, I've replaced both front wheel bearings (were beginning to go bad), changed all diff, t-case, and tranny fluids, put new rotors and pads on + bled the system, and greased both driveshafts but still haven't figured out what the sound is.

U-joints appear to be ok, as do the rear wheel bearings because I'm not getting any noise from them. If anyone can shed some light on this I'd appreciate it!

[Acorn22]

Nobody's got any ideas?

[johnbyebye]

Does this noise occur at any speed when you let off the gas?

When I had this issue with my previous vehicle it was the pinion bearing going out.

[vukos]

See this thread for what may be a similar noise that only appears on coasting: What is this noise?!

I had to get the drive shaft lubed to get the noise to go away

[thegipper]

On face value, it sounds like something in the differential. You can disconnect the rear drive shaft and drive in 4wd, if the noise goes away, then its something in your rear differential, most likely pinion or carrier bearings.

When you drained the diff fluid, how did it look?