The noise when letting off of the accelerator could be one of many things. The motor mounts could be broken and the motor moving into something. The engine belts could be worn and noisy, or several other things. Look carefully under the hood for any sign of wear or parts touching together.
sounds like the alternator is going bad.
Check your Brakes or have someone look at them.
it may be the drive shaft u-joints if its rear wheel drive
Check all your u joints, drive shafts, transfer case and differential oil levels. It sounds like something is loose, the reason you cannot hear it when you accelerate is because of the stress on the parts being applied by the accelereation, it tightens things up, when you let off the loosen up in the available slack in the worn parts.
Poor tire alignment.
could be a vacum leak in the engines intake or just road noise from the tires you cant hear when you step on the gas.
It's one of your vacuum hoses. It's a very common thing to replace
Yeah, it sure is. What is that?
Spray belt dressing on your fan belts
Without pulling codes, I would quess the Oxygen sensor is weak and needs replacing.
If it's a clunk sound, check universal joint bearings and drive shaft bolts. Otherwise please describe noise.
Check your oil level.