sshhlexus

'93 LS400.

This is since I've had the car and it does this only sometimes. If you depress the accelerator in small increments it does not happen. If you're going at least 30mph and you depress the gas gradually one may hear the humming/whirring sound. It is not too loud. Whenever I hear it, I let go off the gas a bit and it stops right away. Seems to be coming from the engine compartment on the passenger side.

Has anyone seen this crop up before ?

It does not have the tell-tale sound of engine knock. Unless the LS400 makes a different sound, if knocking is a problem.

Thanks.

LScowboyLS

what if you are stationary in park and you accelerate to that same rpm?

steve2006

The power steering pump and alternator are located on the passenger side of the engine so it may be worth checking those.

AndyTTT

Check the heat shields over the rear mufflers. I had a similar noise and would have sworn it was coming from the front. When I had a real good look all over the car one of the rear heat shields was loose and making a humming / buzzing noise at certain revs. Maybe not your problem but worth a look?

LScowboyLS

remove the main serpentine (drive) belt and take the car around the block to the speed where it makes the noise and see if the noise is gone now, don't drive like this for more than 10 minutes or so and make sure headlights are off and you have a strong battery

if the noise is now gone, then one of the following is the issue:

● drive belt
● alternator
● power steering pump or pulley
● A/C clutch, pulley or pump
● idler pulley bearing
● tensioner bearing
● fan bracket pulley bearing

sshhlexus

Hey thanks for all the replies.

I have not tried it yet in park and revving.

I just had the steering canister O-ring replaced by my mechanic (incidentally, the steering now is a lot lighter, I’ll have to check the leak area today to see if the job was done good).

The heat shield check is easy enough, as much of the underside is in various states of rust.

I’ll try the belt removal test, over the weekend, if I get a chance.

The noise, when it happens, is low in pitch. And it is very infrequent.

If there is no risk of any damage, I can probably live with it.

sshhlexus

The humming has not happened again, since I posted this, under normal driving circumstances. I have not attempted to muck around with any of the belts. Sometimes I can hear the belt or pulley when in drive idle, like a typical pulley noise, which I don't think this is related to the hum. Now it's like you have to listen real careful for any noises, with windows open. Otherwise the car is very quiet, you can't even tell it's running depending on the other traffic noise.