Everything is fine, no irregular sounds till high up in the rev band. Sound is like someone blowing bubbles in a drink with a straw. This is my second motor in my 98 4.6 and warranty is coming up. If you rev it up standing still on sound. Only under load, heavy footing on the on ramp, using all it has,

 

My experience w/ the piston slap is that is sounds almost like a rod knock when you start the truck. It is a very prominent sound, that if you haven't heard, you don't have.

good luck
Darin

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97 F150 Lariat 4X4 Ext. Cab. 5.4, AT, Gibson Side Swept, K&N, Bosch Platinum +4's (Both doors cracked:-( )