I have a 2003 4.4i 80K miles, yes there is that hissing noise from underneath and from what I read its normal at cold startup. But I drove the truck onto ramps and listened closely and under the transmission Oil Pan I guess I hear "gurgling" noise like transmission fluid is boiling, I can't figure out where its coming from, its a bubbling/gurgling noise. I have no transmission shifting issues or delays or anything like that. Anyone out there have a clue? Could it be low transmission fluid somehow just a tad bit low thus maybe air is inside and gurgling? Thanks in advance. BTW I used my Peake OBD tool and no codes.

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2003 BMW E53 X5 4.4i - M62 engine (Non Sport with Premium and Cold Weather Package)
Color: Steel Gray Metallic
Mods:4.6is Exhaust (Pipes, Mufflers and chrome oval tips) BMW Sport package Taillamps, BMW Tire Valve Stem Caps
Medium tinted front windows
JVC HD Radio
Alpine 4x100 channel Amp
Orion 600W Mono HC Amp
Three 12" Sony Xplode in subwoofer enclosure