Drone between 43 and 57mph, 1997 Previa S/C

[SamPrevia]

Hello guys,

I need help. My Previa makes a low continuous humming sound when the speed reaches 43mph. This drone continues at the same decibel level until 57mph. Once past 57, the sound completely disappears.

It's not loud, but it's definitely there and it's somewhat annoying. It appears to be coming from either the engine or the drive train and it appears to be from the front or directly below front compartment. It does not appear to come from the rear end.

What is it?

Thanks,
Sam

[pdgizwiz]

SADS? Could be a resonance phenomenon.

[SamPrevia]

Thanks for the response, pdgizwiz. I don't know. How do I test and verify it? My Previa has 107,000 miles on it. Is it too early for the SADS to wear out? Or is it more age - 18 years old - related?

A shot in the dark: Can weak struts result in this resonance drone? I know for a fact that my struts are weak and in need of replacement.

[timsrv]

Not struts. Does the sound change or go away if you pull it into a lower gear?

[SamPrevia]

Good question. The transmission was always in "D". I will try to turn off overdrive and report back.

[timsrv]

At that speed range (especially the low end) you could even pull it into 2nd gear. I'm just trying to figure out if it's affected by engine RPM, related to a specific gear, or a specific speed range only. Tim

[ghostbuster88]

I had that same problem on my 94 Previa. when it hit about 60 mph it disappeared till it slowed down between the range you specified. Replaced the wheel bearings and never heard it again.

[TheMAN]

either wheel bearings or rear end noise... check the condition of them and have someone riding in the back to try to localize the noise

[SamPrevia]

I had that same problem on my 94 Previa. when it hit about 60 mph it disappeared till it slowed down between the range you specified. Replaced the wheel bearings and never heard it again.

Thank you ghostbuster88. Which wheel bearing (left or right) did you replace? How many miles did your 94 Previa have when the bearing(s) failed?

TheMan: When I get a chance, I will seat in the back to check out the rear end noise. Thanks.

[pdgizwiz]

If it's the SADS, this might help confirm it:
Get going down a straight road until you hit the speed at which the noise begins. Turn the fan on low, and switch on the A/C. This will change the load on the SADS. Does the noise stop?

If it's the rear end, it will be load dependent. Does it come and go if you step on the gas a bit, or let off? Same if you start up or down an incline.

If it's a wheel bearing, it might change as you round a corner. So find a road where you can get to the noisy speed range without any traffic, and weave a little side to side without changing speed or load. Does the noise change from turn to turn?

I've found that bad wheel bearings will make more noise is the wheel is unloaded. For example, a bad right wheel bearing will howl more if you are taking a right hand turn. The right wheel is on the inside and the load is shifted to the left. Your results may differ, or course!

I think that as you guessed, a SADS goes bad with years rather than miles. Rubber parts just get hard and fracture. You'll have to get underneath to check, and know what to look for.

[SamPrevia]

At that speed range (especially the low end) you could even pull it into 2nd gear. I'm just trying to figure out if it's affected by engine RPM, related to a specific gear, or a specific speed range only. Tim

I turned off Overdrive today and it makes no difference. Still the same drone between 43 and 57mph.

Now I need to know which front wheel bearing (left or right) is making the noise. Assuming of course it's one or both of the front wheel bearing. I haven't found a safe road on which I can try loading / unloading one of the front wheel yet.

[ghostbuster88]

I went and replaced both. With parts that wear evenly together, it's always good to replace both. Ex: tie rods, ball joints, etc