Between the speeds of 9 and 12 miles an hour my truck will make a thump noise. I am a rural carrier and much of my time is spent going from 0 to about 20, so I constantly hear and feel this as I go from box to box. The sound is coming from the rear and I can feel it. It is not the transmission.
More info…kind of truck, 2 or 4wd? Noise consistent with speed of truck? Possibly a U-joint?
Also, exactly what conditions cause the thunking?
Is it a single thunk or does it begin a thunking pattern?
And does it seem consistant with the speed of the wheels or not?
And is this a manual or an automatic?
Due to lack of feedback I guess Ujoint, more guesses? Thank goodness it is not the transmission, how do you know? Farther back leads to differential, could even be a sticking brake pad, so many choices.
Since you are a rural carrier I guess you are driving your own vehicle. I’ve tried to imagine what sort of truck is appropriate to this kind of work unless you have modified your vehicle to right hand of the road driving. You need to let us know what your vehicle is, and what has been done (if anything) to the vehicle to help you deliver mail from the right side of the vehicle.
The thread is tagged Toyota Tacoma, but we still need more information to start speculating on the issue. Year? 2wd or 4wd? Mileage? Manual or automatic? Better description of the noise and when it occurs? Does the noise sound rotational? Single thump or repetitive thump? Too many unknown variables.