One problem related to engine noise has been reported for the 2001 Ford Explorer Sport. The most recently reported issues are listed below.
At 2100-2300 rpm on acceleration a pinging sound is heard that sounds like spark knock (detonation). The actual cause is from defective timing chain guides which allows slack in the timing chains (4. 0 engines has one in front and one in rear) and is causing it to rattle and eat away at the guides. This is commonly known as the "rattle of death" on the Ford 4. 0 engines because once the plastic on the guides gets eaten away by the loose timing chain, it eats into the metal support and create metal shavings throughout the engine which will cause failure, if the chain does not fall off first. This is a well known and well documented problem due to cheap timing chain guides.