A little more info would help. For instance what engine the van has, where the noise is coming from, etc. For now all I can do is guess based on a spray can rattle. Try checking your oil and see if it's low. if it is, it usually causes your engine to knock a bit.
1999 Chevrolet Camaro SS (PC'd)
1994 Chevrolet Beretta Z26 Q4 (W41 M90'd)
2004 Chevrolet Silverado 2500 (4WD)
My wife's cars:
1971 Dodge Charger SE (stock and original 383 auto)
2004 Subaru Impreza WRX (kid-hauler)