Valve clearance is the distance between the end of the valve stem and the end of the valve lifter mechanism (also known as valve lash). If excessive, can produce a tapping or clicking type of noise, usually louder when things are cold. If present with hydraulic lifters, something usually needs attention or repair. If solid lifters, usually can be adjusted to mostly eliminate this noise. Believe you've got hydraulics, so if they are making this kind of noise, may be worn out or leaking down. However, hard acceleration should not markedly increase the noise level, it should just get quicker. You may have more than one thing going on here.
2000 Dodge Grand Caravan SE