Low Humming under Acelleration

[gmenor]

Driving back from Virginia today I noticed a low humming soundand ver little vibration. Couldn't really isolate it doing 70 mph going south on I-95 - but it was coming from the engine compartment (or vibrating from the transmission). Everything was normal, trans temp, egt and boost. All guages read as usual, voltage, temp and oil pressure. I thought I cured this humming by changing out the u-joints. All this was at 70 mph @ 2250 rpm under acceleration, cruise control on and off. Stop to top off at the VA-NC state line and the noise was not as noticable. But under hard acelleration it came back. This only occurs over 60 mph. The humming sound - sounds like an turbo prop aircraft. Any suggestions would help as a starting point.

[gvig]

Just had a similar noise in my pickup. Couldn't put a finger on it but it occured under light to moderate acceleration or steady running at higher speeds when loaded. Turned out to be a failed rear pinion support bearing in the differential. Rollers were already melting into funny looking shapes :eek:

The cure was obvious. The rear of the pinion was gone so a new gear set was indicated. Blumenthals in OKC had a 4.10 gear set and a bearing set too.
They only wanted money for me to walk out with them :(

Hope yours is easier and less expensive.

[Eric Selinger]

Check to make sure your inner fender mud guards are not torn or have come unpinned and may be rubbing on the tire at these speeds.

Good luck!

Eric

[gmenor]

Thanks all didn't think about differentials or d flaps. Both can be checked easily enough.

[DA BIG ONE]

I'd check the fan clutch, sounds like fans clutch is engaging. I had this problem and thought that my aftermarket bumper/brushguard caused some of the issue. But, the bigger problem was lots of dirt, bugs and other ___ caught in and between the oil/trans coolers, ac cond, and radiator. Made tool powered by high pressure air to clean it from the inside out. No fan clutch engagement now, even after putting back the brushguard cross bar in front of radiator on the aftermarket bumper.

Another thought: Have a bug deflector?

I remember some issue w/bug deflector mounted on leading edge of hood would cause the trim around windshield vibrate at speed, the fix was use strong and black weather strip glue for the trim.

[gmenor]

Da Big One,
My temperature stays below 210 for the fan to engage. Temperature is the least of the problems while not towing. I plan to have friend drive the Burb and chase it with my wife's car to see if there is something going on that I can't see.

[DA BIG ONE]

If your 4wd check the front diff bushings to see if there is any metal to metal contact under torque condition.

Then there is that trusty exhaust down pipe hitting the chassis, or back pipe hitting x member when the motor mounts get weak. This is one of my main issues, mounts don't last more than a year in my case and they don't make poly mts for my truck.

Anyway, good luck w/it and let us know what you find.

[1bad383]

Something else to think about, the driveshaft center support bearing. Mine sounded like the gears going out for a while, then sounded like a front passenger wheel bearing (2 wd) going south. Both were fine. The center bearing outwardly looked fine untill I gave it a good shake, and it had a bunch of slop in it. Seems like the bearing lasts for about three years, or about 70 K miles.

[gmenor]

I just recently changed out my third (??) set of front rotors and wheel bearings - warping issues. I am having the tie rods changed out and I am waiting on some shocks that I ordered from JK. The shocks are still stock. The down pipe has a lot of clearance and mounts still holding up fine. I'm fixing to leave town next week for about a month so the truck will get painted in my absence. I don't what GM has done but my entire body is fine except for paint flaking off or clear sealant is flaking off.