I'm starting to notice a popping noise coming from it sounds like the throttle body,I only hear it after trucks been sitting for awhile like in the morning or after work,I do have the K&N fipk and I'm sure it probably has something to do with that.It happens after truck is started and it only for a second almost like something is opening kinda like the sound you hear when your vent closes anybody else have this or have any idea what it might be.everything looks fine with the K&N.Thanks in advance.

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99 F250 XLT LD 4X4 S/C,5.4,3.73 Limited slip,Bright red clearcoat ,4whl abs,remote start w/keyless entry and alarm,chrome rims,tinted,westin nerf bars,factory tonneau,superchip,K&NGen II fipk,pioneer in dash cd,pioneer amp,infinity kappas all around,Lund front runner bug sheild.Gibson split rear,stull SS grilles.