Weird clunk and humming

I have a 98 S-10 ZR2 4-wheel drive truck.Sometimes when I put the truck in reverse and cut the wheels,I hear and feel a clunk.The noise seems to be coming from the front?????It only does this when the truck has sat for a little bit.The u-joints look good and has new front wheel bearings.I don't get it.I also have a noise when driving down the road.The noise is like a humming and comes in at about 45mph and leaves at about 63mph.I put the tranny in neutral while coasting and the noise is still present,turn the wheels and the noise is still there.I can also feel a light vibration in the wheel.By the way,it is not tire noise.I know that sound.Please Help!

might be a front cv joint

I think I can help you with the humming noise. My truck did the exact same thing. The first time it happened I pulled over immediately because it sounded like i had a flat right front tire. After a lot of cursing I found the problem. There is a vacuum switch on top of the transfer case with three hoses going into it. It was worn out and sticking open when it shouldn't be. So that humming noise you're hearing cruising down the road is actually your front hubs trying to engage....not good. You can find the part at the dealer for less than $50 and I think it was called the transfer case control valve or something like that. It's a rare part and I had to really push them at the dealership to find it for me, so don't let them give up on you. If your hands aren't too big and you have a good assortment of tools, you can replace the part without having to move anything out of the way. Good luck!

Check Your Suspension Bushings. There Are Too Many Possibilities When It Comes To Clunking. I Have Seen Control Arm Bushings, Sway Bar Bushings, Steering Arm Bushings, Motor Mounts All Make Noise And There Is No Way To Determine Where The Noise Is Coming From Unless Someone Goes Under The Car And Starts Testing The Bushings By Stressing Them With The Breaker Bar. The Same Issue With The Humming Noise It Could Be Any Bearing Under The Car. There Are Too Many. You Will Have To Jack Up The Vehicle Getting All 4 Wheels Of The Ground And Run The Truck While Someone Is Under There Trying To Find Your Humming Noise. Some Bearings Require A Load To Make Noise Such As The Front/rear Wheel Bearings But The Trans, Transfer Case, U Jounts, Etc You Should Be Able To Hear. Good Luck!

U joints in the rear and your front steering aseembly and tie rods etc need to be greased.

I was in a another ZR2 and the clunk was present in it too,it had like 35,000 mile on it.So it must be a S10 trait?

No, it is NOT a trait.