Detonation maybe?
What kind of gas are you running?
My 00 SVT does not like Sunoco or Speedway gas as they contain more Ethanol (supposedly). I've had knocking or pinging when I used their gas once. Never again.
COuld be a sticking valve. Has it had the oil changed recently? If not, do an engine flush, put in teh Mobil 1 synthetic, and substitue 1 quart for a bottle of risoline. So, that would mean 5.5 quarts fo mobil 1, plus 1 quart of Risoline. Stuff works EXCELLENT for unsticking noisy lifters and you don't have to flush it out, until your next oil change (3-5K miles)
Valve lash or anything you are discribing doesn't usually just make a coupel noises and then dissapear.
