#1 you are posting on a thread thats three years old
#2 need to know what year mustang you have, 'older' covers about 50 years
#3 start a thread giving year, engine and any modifications to the car along with when/how the noise is heard/felt
Actually the thread was 12 years old, then got a reply making it now 5 years old, and now revived in the current day. Just helping with your math. Carry on......