Pulsing, echoing, vibration only when accelerating

[SOTF]

It is a deep vibration sound, fairly loud drone. Only occurs when foot is on pedal. It is not RPM dependent but the drone becomes louder after 65-70, peaks about 75 mph. It is a very loud, pulsing drone that I can feel inside the vehicle at these speeds. It immediately goes away when my foot is off the gas. Starts again right when I'm accelerating/foot on gas. I can hear the drone at lower speeds too. It sounds like it's coming from the front left. Here is the thing - this just started a few days ago after I did the following:

My front left diff mount was completely missing the top spacer. I replaced both front diff mounts with the whiteline bushings. I left the OE bushing on the rear mount as it seems to be in good shape.

The previous owner or owner's mechanic miffed up a lot of stuff on the left LCA. The ball joint was dry. The inner CV boot on left side was not clamped and was spitting grease. The left LCA was not torqued properly, causing the clunk on a reversed right turn. I cleaned up the CV axle, re-greased and clamped boot. I greased the ball joint, re-torqued LCA which fixed that loud gunshot-like clunk on the reverse.

I replaced all KDSS/sway bar bushings on the front.

I hope it isn't the front left diff mount bushing I replaced (poly)?

This noise only started after I did the mentioned in the previous days. The pulsing drone at 70-75 mph is so loud in the cabin I am not comfortable driving at that speed. Funny enough, the pulsation seems to even out into a straight, loud drone after 80 mph. DOO - DOO - DOO - DOO - DOO or WOO WOO WOO WOO WOO. I will try to attach a video of the sound if my phone picks it up.

 

[SOTF]

also no difference in sound when doing a slolem for wheel bearing

 

[joabmc]

Completely unrelated to the work you performed but I’d be looking at U-Joints.
Sound has a weird way of bouncing around under the vehicle.
-CVs usually have a clicking sound
-bearings can be isolated in a slalom test.
-you could jack the front end up and check the 12 & 6 for bearing play
-9 & 3 for ball joints and end links.

 

[SOTF]

Yeah, no play in any direction on the front wheels nor an audible difference when slalom testing. I was leaning towards u-joints but seeing as the sound was not there the day before I did all the fixes and there afterward, I was trying to look past coincidence.

 

[joabmc]

Yeah, no play in any direction on the front wheels nor an audible difference when slalom testing. I was leaning towards u-joints but seeing as the sound was not there the day before I did all the fixes and there afterward, I was trying to look past coincidence.

I agree but it sounds like you have inspected the front in thoroughly. And the clue that it disappears when there is no load on the drivetrain led me to u-joints. But I’d definitely go back retrace your steps as it didn’t start until you worked on the front end. Good luck and be sure to post your findings. It’s always helpful.

 

[SOTF]

I agree and will do.

 

[SOTF]

I greased all driveshaft zerks and checked front end for play and nothing of note. the sound is steady drone at 45 and around 75 is a loud pulsing drone. It definitely sounds like it's right below and in front of the driver I know sound can be weird but it I'm rather sure it's in front left.

 

[joabmc]

Hmmmmmmm! Not noticeable at lower speeds... Did you try throwing it in neutral, at speed to see if it goes away then? So many little components in the front end of these, sometimes it's hard to isolate. Feel anything different in the pedal or steering?

 

[joabmc]

Did you double check the CV that you worked on for play?

 

[SOTF]

Hmmmmmmm! Not noticeable at lower speeds... Did you try throwing it in neutral, at speed to see if it goes away then? So many little components in the front end of these, sometimes it's hard to isolate. Feel anything different in the pedal or steering?

There is no sound the second I let off the gas pedal. The moment I press the gas, the sound returns so nothing in neutral. The sound is there at low speeds but it is just very quiet. The faster you go, the more noticeable it becomes. It is steady, then begins to pulse after 70. It is loud but my phone isn't picking it up well. The front left CV has play where it goes into diff but it is slight. Something is definitely miffed with the front left end. As I previously said, there was no upper spacer on front left diff mount. That spacer is encased in metal and it was completely missing so someone removed it imo.

The play is like in this video but not nearly as bad. It seems like his fix was a clamshell bushing. From what I've read, there is slop in the OEM needle bearing so I do not think that is my issue.

 

[joabmc]

There is going to play on one side. Not that much by any means but depending on torque, one side will be tight and the other will have a little bit of play as it isn’t engaged.
The CV axle is the intentional week link in the chain. I hope there isn’t damage to the diff. due to the missing bushings. If all componants are tight, you may have to dig a little deeper into the diff.

 

[GXO]

AWD GX470s and AWD FJs and 4Runners do not have a needle bearing.

 

[SOTF]

Alright. Is it possible the poly bushings I replaced for diff mounts are allowing additional harmonics from a previous problem to now become audible? Given how this sound began right after changing them sounds possible. I will say on the front left differential mount, there are 3 bolts that go into diff and require 137 ft lbs torque. The upper one seems impossible to access with a socket without dropping diff so it is not torqued properly. However.. it is awfully tight. Will be using crows feet to check that.

 

[vwynn]

ive noticed a WOO WOO WOO WOO sound when accelerating around 70-75.... Gunna lurk this for answers hopefully.

I feel/hear it near the driver side footwell.

 

[missouristig]

I have a similar feeling. It's definitely right about 75 and when i'm accelerating. It's a vibration in my feet in the driver's side but nothing through the steering wheel but there is a definite noise. But it's pretty minor. I figured it wasn't anything major and just chalked it up to something hitting just the right frequency but i'm open to solutions.

 

[joabmc]

Any updates?

 

[SOTF]

Nope, cannot find the source. It sounds like it's the front left wheel area for sure. I was incorrect - when I slalom the pulsing sound changes but it's louder when the right wheel is loaded. At 75 mph it sounds like a loud pulsing rubbing sound. The changes in sound would indicate a wheel bearing but it's on the opposite side of what the slalom test would indicate and the sound stops immediately when letting off the gas pedal. I've had wheel bearings behave oddly before but not in this manner. My sound is very loud and I can feel it. I wish my phone would pick the sound up. It sounds like a hovering flying saucer. WHOOM WHOOM WHOOM WHOOM WHOOM is a better description than "WOO WOO WOO" from the front left tire area but gets louder at 75mph when the RIGHT side is loaded. The right side also had a seized caliper piston which I rebuilt yesterday. I am not so sure the sound could transfer from a bad right wheel bearing all the way to the left and be that pronounced. It FEELS like it's to the left of me and it becomes much more audible the closer you get to the left door panel/steering wheel.

I am going to be doing a lot of front end work including wheel bearings, all bushings, ball joints etc as this is an offroad project. I fear I'll end up fixing it in the coming days without knowing what the problem was, which is bothersome.

 

[GXO]

I've seen bearings make noise unloaded.

 

[SOTF]

Been busy so I haven't driven or worked on this vehicle. Although I changed the driver's side CV a few days ago. The gx470 is still making that pulsing sound but now there is an additional symptom only when accelerating. A very intense shudder/vibration when accelerating. It feels and sounds like I am driving over rumble strips whenever I have the gas pedal depressed. Not bumpy, but the vibration is similar. Very tightly packed rumble strips as the vibration is quickly paced. Acceleration is also labored. I need to floor it as it feels like I am dragging something. No sticking caliper. Sounds like it's from the front. Will be changing wheel bearings and u-joints. From brief research, I see some people with "rumble strip" 4runner issues. Torque Converter? Might be a different issue as this is only under load. This is at every rpm, regardless of gear. Although it is hard to notice at slower speeds and light acceleration. Neutral doesn't make it go away as it's only under mild+ acceleration. I'm betting it's a bearing or u-joint but eager to figure it out. The vibration is quite aggressive. Feels like I'm dragging a brake pad.

 

[GXO]

Torque converter sounds likely. I would do a drain and fill and inspect the fluid in the trans and tcase. I would also check your caliper pistons. They are notorious for sticking/freezing.