1999 SC300 Humming in Top Gear

Quote:

Noises are difficult to identify without actually hearing them. Check yhour tire pressure to make sure the tires are properly inflated. Check the condition of the transmission fluid - is it brown or smell burnt? Does the humming sound change if you are in 4th gear but tap the brake pedal enough to disengage the torque converter lock-up? Does the humming change when accelerating or decelerating in 4th? What road speed range? What engine RPM range?

Thanks for the response, Ray.

The tires are properly inflated and new.

The transmission fluid looks fresh. I'm guessing they replaced the transmission fluid at the dealership.

Actually, I did some experimenting and it's not just in 4th gear.

It seems to start at almost exactly 40mph and stays for anything higher.

Acceleration/deceleration and engine RPM don't seem to make a difference.

Might it just be normal roud noise from loud tires or coming from the suspension?
 >> Stay informed about: 1999 SC300 Humming in Top Gear 

"thoffen" <UseLinkToEmail.TakeThisOut@AutoForumz.com> wrote in message
news:1_636719_870a071b8d248000f97995581b26febe@autoforumz.com...
> >
>>Noises are difficult to identify without actually hearing them.
>>
>>Check yhour tire pressure to make sure the tires are properly
>>inflated.
>>
>>Check the condition of the transmission fluid - is it brown or smell
>>burnt?
>>
>>Does the humming sound change if you are in 4th gear but tap the
> brake
>>pedal
>>enough to disengage the torque converter lock-up?
>>
>>Does the humming change when accelerating or decelerating in 4th?
>>
>>What road speed range?
>>
>>What engine RPM range?
>>
>
> Thanks for the response, Ray.
>
> The tires are properly inflated and new.
>
> The transmission fluid looks fresh. I'm guessing they replaced the
> transmission fluid at the dealership.
>
> Actually, I did some experimenting and it's not just in 4th gear.
>
> It seems to start at almost exactly 40mph and stays for anything
> higher.
>
> Acceleration/deceleration and engine RPM don't seem to make a
> difference.
>
> Might it just be normal roud noise from loud tires or coming from the
> suspension?
>

Several clues point to the tires as the cause of the humming.

First, the tires are new so they are the biggest variable in the car.

Transmission, engine, and driveline, bearing noises tend to change with
engine RPM, road speed, acceleration, deceleration, temperature, etc.

Tire noises tend to become noticeable at a certain speed and road surface
and stay about the same volume but may change in pitch with speed. Tires
tend to be noisier on concrete surfaces than on asphalt surfaces.

There is a catch-22 when driving a really quiet car like the LS or SC, and
that is that noises that might ordinarily be drowned out in background noise
becomes noticeable.

You can confirm that the tires are causing the noise by driving on several
different road surfaces, i.e., concrete, asphalt, gravel and see if the
noise changes.
--
Ray O
correct the return address punctuation to reply
 >> Stay informed about: 1999 SC300 Humming in Top Gear 

That POP sound you hear is normal from every SC. Simplified: it's the sound of the brake pads popping off the rotors when you change from D to R, or R to D. It's completely normal, happens with every SC.

BTW I own a 1994 SC3, I'm just here on this forum for my Volvo, for Lexus forums I use http://www.clublexus.com

Edit, as for the tires, have them re-balanced at any discount tire shop, and see if that fixes your humming.
 >> Stay informed about: 1999 SC300 Humming in Top Gear