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My 2006 Nissan Titan makes an odd sound, like a grinder, mostly when travelling steady at 35, 40 or 45 miles per hour. Even 1-2 mile per hour difference will cause the noise to stop.

The noise will go away if I accelerate slightly or slow down by letting off the gas. I've noticed that it will also make the same sound around 20 miles an hour, sometimes when turning, sometimes not. It will not make the sounds during steady acceleration passing through 45 miles an hour.

Could this be a wheel bearing, or possibly the fuel pump? It's a difficult sound to locate whether I'm a passenger or driving, as I have a custom exhaust that's rather loud.

Thanks for the ideas!

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If it is only at those speeds then there is a resonance somewhere. Do those speeds correspond to a specific RPM? If so then there is something related to engine speed - perhaps mounts. If it is not related to RPM then check wheels, shocks, bearings etc –  Rory Alsop Mar 16 '13 at 18:09
    
I'll definitely check and see if it corresponds to a specific RPM. –  Brandon Mar 16 '13 at 18:12
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2 Answers

I would imagine that something is just rattling.. I say this because if it was an issue of possibly a pulley or a wheel bearing or anything at all for that matter. Then the noise would be more consistent. It isn't too often where you have a vehicle that only has an issue in that tight of a situation.

mostly when traveling steady at 35, 40 or 45 miles per hour. Even 1-2 mile per hour difference will cause the noise to stop. The noise will go away if I accelerate slightly or slow down by letting off the gas. I've noticed that it will also make the same sound around 20 miles an hour,

This leads me to believe that it's an issue of something vibrating. At a stead 35 to 45 miles per hour the engine should be I'd say about 2500rpm on the highway. Around the same rpm that it would be at when coasting 20 miles per hour. A slight increase in speed also is directly related to a slight increase in RPM, and the noise is gone. Turning, (lets build a scenario of you turning right at a read light) you touch the gas slightly and turn. Most likely hitting right around that 2300-2500rpm mark to get the noise to occur.

Next time you're in the vehicle and you hear the noise take note to where in the RPM range the motor is at at the given time. Then when you get back to your parking spot try to replicate the noise while stopped. If you cannot get it to happen while stopped then perform the following test.

Fully engage the parking brake, place the vehicle in drive, and place your left food on the brake pedal. Then with your right foot start to bring the RPM level up (use common sense here, don't just put a brick on the gas pedal because you'll end up slamming into whatever it is in front of you).

Using the second method if the first one fails will ensure that all the components are engaged and being torqued as if you were driving the vehicle down the road. You'll feel the entire car lurch up (resembling a cat ready to pounce).

If you can get the noise to reoccur at will then you can have someone assist you in pinpointing it's location.

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Thanks for the ideas. I'll try the parking brake/brake/gas method - with a lot of room in front of me - this truck has 313 HP :) –  Brandon Mar 17 '13 at 12:06
    
If you get a chance, slide under the truck and make sure that the the heat-shields around the exhaust aren't touching on the exhaust. This usually happens from going through a nice puddle. They're made of a rather thin aluminum so you can just push them back with a long flat-head screwdriver or if you can reach them safely then just use your hand. –  cinelli Mar 17 '13 at 21:58
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I wouldn't describe a vibration as a "grinding" sound. Usually you would hear a rattle or ping. Grinding makes me think something that is rotating. I guess it is possible that something is intermittently touching the driveshaft? –  Mike Saull Mar 20 '13 at 16:17
    
It's also possible the noise wasn't explained correctly. When giving my answer, tried to think of the symptoms given and forget about the description of the noise. I can see see how a low pitched heat-shield could be processed as a "grinding" noise to a customer. Do you agree? –  cinelli Mar 22 '13 at 14:01
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@cinelli Yeah I agree its possible. Just if you are looking for "grinding" specifically that isn't where I would start looking. If you disregard the description of "grinding" then you have to start looking at suspension springs, bushings, shocks etc the list of possibilities goes up like crazy. –  Mike Saull Mar 22 '13 at 15:32
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Wheel bearing was my first thought but it should get louder at higher speeds and remain during accel and decel.

possibly some issue with the torque converter not locking or slipping at certain speeds? Does it only happen in the highest gear of the transmission?

the turning at low speed leads me to think power steering pump. The sound should change with engine rpm. Try revving the engine at different speeds in neutral.

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The sound stays constant in volume, no matter which speed, and only happens at the specific speeds. I'll check to see which gear I'm in when it makes the noise and also check in neutral. –  Brandon Mar 16 '13 at 18:16
    
An issue with the converter lock-out clutch would give a feel similar to a failed Mass Air Flow Sensor. The steady jerking or bucking at a constant cruise speed on the highway, or a slight load when going uphill at highway speeds. –  cinelli Mar 22 '13 at 14:03
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