Low pitch hum

[user 62785]

Now that the weather is cooling off I'm hearing a low pitched (but loud) hum seeming to come from the drivers side of the engine compartment of my 2wd 01 job 1 ST (60k miles). The sound seems to be most pronounced starting at around 40mph (around 2k rpm) but seems to gets drowned out by engine and road noise at around 55 or 60mph. I tried an experiment to determine if the noise was RPM-based the other day. I put the auto trans in park and revved the motor to 3k rpm and held it there for a few minutes but got no noise.



I checked my tires (Michelin LTX) and they look ok (have around 5/32's tread left and were balanced and rotated around 2 weeks ago). Brake noise is around normal levels (they squeel when braking in reverse and make more noise in the mornings when they're cold). I don't see much play in the wheels and get no sound from them when the truck turns corners so I'm thinking this is not a wheel bearing drying up or going bad. I've read here about the issues with seals on the axle but all seemed to reference 4x4's and not 4x2's.



I thought that maybe it might be the alternator but I didn't think the alternator was on the drivers side. I'm also not seeing visible evidence to indicate that the truck is struggling to generate power. Given that I'm not very mechanically inclined I'm running out of ideas of things to check. :unsure:



What am I overlooking? I suppose I could take the truck in to the shop but I just don't like not knowing what the problem might be... well that and the fact that taking a vehicle to most Phoenix-area Ford dealers this time of year means leaving it for two days till they get around to looking at it.



Martin

 

[Andy G]

I had a wheel bearing start to hum on my Jetta, the wheel had absolutely no play in it what-so-ever, but the bearing was going out.



It was very deceiving. Although, it got much louder (and higher pitched) at higher speeds, which doesn't seem to play into your symptoms very well.



I have also seen output shafts (output bearing)on trannys make a similar noise. As well as drivelines or u-joints that are on their way out.



Check your driveline, that is what I would do next. Crawl under and shake it, see if it feels loose.

 

[Johnny O]

I'd look at the wheel bearings first. Tires can get noisier as they wear down. My Ranger was so loud I took it to the dealer, they couldn't find anything, swapped tires with another Ranger that was on a lift, drove mine around the block, and no noise.

 

[user 62785]

Thanks for the info! The source of this noise is definitely a bit puzzling to me. I've checked all of the obvious things (at least to me) but it seems to be a more obscure issue.

 

[user 62785]

Well I've now validated that it isn't my tires. I found a set of 5-spoke 16-inch FX4 alloy wheels on Fleabay that happened to be sold by a seller here in Phoenix. I bid on them, won, and picked them up today. Downside is that they happened to have brand new Crapyear Wrangler RT/S's on them but I suppose I can deal with them for the next year or two.



Mounted the tires and took a test drive... noise is still there though it seems quieter than before. Oh well at least the tires look better than the stock steel wheels! And I can finally see my painted (so I didn't have to look at rust colored) calipers any more...



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