I recently bought a 92 pickup SR5 with 300 000km and have an issue that I'm having a bit of trouble tracking down. I'm use to front wheel drive cars, so it could be something pretty obvious, but it seems like a wheel bearing to me. Occasionally ill get a slight vibration that almost sounds like i'm driving over a very small rumble strip in the road. It seems to be coming from the front drivers side, but its hard to tell. It isn't tied to any particular speed or gear though does seem to be more noticeable between 40-70 kilometers an hour, but i assume that's because it becomes harder to hear once I'm up to speed. it will pop up randomly and last between half a second and maybe 3 seconds before going away. Taking my foot off the gas usually gets rid of it, along with bumps on the road. It does seem to be worse when it's cold outside, and will only happen about half the time that I take the truck out. It does seem to be worse within the first five minutes of driving.

The wheel seems tight, without any obvious play and the front end doesn't really have any other strange noises while driving. Thanks for any suggestions. I don't know how to make the picture any smaller, so enjoy!

 

Hard to tell from your pic if truck has ADD system or manual hubs. If ADD first thing to cross my mind would be dry steering knuckle bushings.

 

Some questions and testing you could try:
Does this vibration happen both in 2WD and 4WD?
As stated above, do you have locking hubs, ADD?
Does it go away if you lightly touch the brake pedal? How about when you lightly apply the parking brake?

Find a lonely piece of road so nobody thinks you're drunk and when you get the vibration/noise try weaving side to side (not violently) and see if the noise comes/goes or changes significantly like "goes away or quieter when I turn left". This is often the case when a front wheel bearing starts making noise without seeing much play in it and it may help you determine which side if you can hear it any better. Noisier when turning left is usually the right side bearing and when turning right would be the left bearing because of the increased side load. This is not 100% but it has helped me in the past.

 

Thanks for the input. The truck has ADD, it seems to go away with touching the brake, but usually lasts such a short amount of time that i'm not confident that the braking causes it to stop. It doesn't stick around long enough to try the parking brake.

Ill head out to a quiet road on my next day off and see what comes of it.